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Jul 23, 2019 — This type of peripheral vision distortion can often occur if the new glasses are of a higher prescription or the frames are larger than what you ...

Esco Optics, Inc. 95 Chamberlain Road, Oak Ridge, New Jersey 07438 Tel: 1-800-922-3726 | Fax: 1-973-697-3011Sales@EscoOptics.com

Viewing through an eyepiece is more complicated, because the eyepiece is also a lens system with a focal length that interacts with the prime focal length of the telescope. The focal length of the telescope divided by the focal length of the eyepiece determines the magnification you see. Given eyepieces designed with the same apparent field of view (AFOV), a shorter focal length eyepiece will give a smaller field of view (and greater magnification) in any given telescope.Argument in favor of SHORTER (f/5-f/7) focal length telescopes (by Gordon Landers)For a given clear aperture, a shorter focal length results in a larger photographic f/stop; this means shorter exposure times. For example, a telescope with an 80mm clear aperture and a 480mm focal length is an f/6 optical system; a telescope with an 80mm clear aperture and an 800mm focal length is an f/10 optical system.Short focal length refractors and Newtonian reflectors are easier to store, transport and set-up than their longer focal length counterparts. Short focal length telescopes benefit from an increased field of view. With the excellent color correction of the APO refractor (or any reflector), one of the advantages of long focal length, minimizing chromatic aberration, is obviated.An optician I'm not, but it seems to me that the other advantage of long focal length is less chance of coma and other aberrations when using shallower curves in refractor lens cross section (or reflector primary mirrors -Editor), resulting in a sharper image. Using my short focal length Stellarvue SV80ST APO refractor (80mm aperture, 480mm focal length, f/6) for comparison, my eye cannot perceive any problem there. I have seen more such problems in some oculars than in my scope.It seems to me that the only other concern (regarding short focal length) is magnification limits due to the ratio of focal lengths of objective to ocular. I have another scope of greater aperture and focal length for when I want those advantages, but there are times when I really like the wide field and pinpoint stars shown by my short focal length SV80ST. Examples of that are the views of the Double Cluster and the Pleiades. Obviously, the SV80ST will show less lunar and planetary detail than a larger scope of equal quality, but once again, the APO's sharpness and contrast make for rewarding viewing. At star parties, where I can quickly compare views with club members' Dobs, I am still pleased with the SV80ST. In short, some of the disadvantages of short focal length can be overcome with technology and quality.Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

Short focal length refractors and Newtonian reflectors are easier to store, transport and set-up than their longer focal length counterparts. Short focal length telescopes benefit from an increased field of view. With the excellent color correction of the APO refractor (or any reflector), one of the advantages of long focal length, minimizing chromatic aberration, is obviated.An optician I'm not, but it seems to me that the other advantage of long focal length is less chance of coma and other aberrations when using shallower curves in refractor lens cross section (or reflector primary mirrors -Editor), resulting in a sharper image. Using my short focal length Stellarvue SV80ST APO refractor (80mm aperture, 480mm focal length, f/6) for comparison, my eye cannot perceive any problem there. I have seen more such problems in some oculars than in my scope.It seems to me that the only other concern (regarding short focal length) is magnification limits due to the ratio of focal lengths of objective to ocular. I have another scope of greater aperture and focal length for when I want those advantages, but there are times when I really like the wide field and pinpoint stars shown by my short focal length SV80ST. Examples of that are the views of the Double Cluster and the Pleiades. Obviously, the SV80ST will show less lunar and planetary detail than a larger scope of equal quality, but once again, the APO's sharpness and contrast make for rewarding viewing. At star parties, where I can quickly compare views with club members' Dobs, I am still pleased with the SV80ST. In short, some of the disadvantages of short focal length can be overcome with technology and quality.Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

The meaning of magnification. Definition of magnification. Best online English dictionaries for children, with kid-friendly definitions, ...

Shorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

by K Peters · 2010 · Cited by 610 — Abstract. Polymer optical fibers (POFs) have significant advantages for many sensing applications, including high elastic strain limits, high ...

Astronomical telescopes are typically described by their clear aperture, focal length and focal ratio. The specifications for focal length and aperture are measurements given in inches or millimeters (or both), while the focal ratio is calculated by dividing the focal length by the aperture. Hence, the specifications for a typical telescope, for example the ubiquitous Celestron C8, are as follows: 8" (203mm) clear aperture, 2032mm focal length, f/10 focal ratio.Focal length, the specification of concern in this article, is defined as the distance from the optical center of a lens (or optical system) to its point of focus when focused at infinity. (See the diagram of a simple lens at the top of this page.) The optical center of a multi-element lens system, like a camera lens, is defined as the "rear nodal point" and usually does not coincide exactly with the physical center of the lens system. As applied to telescopes, this definition works perfectly for refractors, since they use lenses to focus light. The focal length of reflector telescopes, which use mirrors instead of lenses, is measured from the first active optical element (the corrector in an SCT or the surface of the primary mirror in a Newtonian) to the point of focus.Since focal length is a linear measurement of the scope's light path, conventional refractors and Newtonian reflectors must be physically at least as long as their focal length. Catadioptric (CAT) telescopes fold the light path back and forth internally and thus are typically much shorter, physically, than their optical focal length. This makes for a relatively short, compact optical tube and gives CAT's a big advantage in portability.The focal length of any telescope (or other lens system) determines its angular field of view. A longer focal length telescope takes in a narrower field of view and a shorter focal length scope takes in a wider field of view. This is easily demonstrated by taking photos through two telescopes of different focal length from the same position with cameras attached directly to the back of their optical tubes at the point of focus. This is called prime focal length photography and the photo from the shorter focal length scope will show a wider field of view, regardless of the aperture or design of the telescopes. In other words, it is focal length that determines a telescope's field of view, regardless of the diameter of the objective lens or primary mirror.Viewing through an eyepiece is more complicated, because the eyepiece is also a lens system with a focal length that interacts with the prime focal length of the telescope. The focal length of the telescope divided by the focal length of the eyepiece determines the magnification you see. Given eyepieces designed with the same apparent field of view (AFOV), a shorter focal length eyepiece will give a smaller field of view (and greater magnification) in any given telescope.Argument in favor of SHORTER (f/5-f/7) focal length telescopes (by Gordon Landers)For a given clear aperture, a shorter focal length results in a larger photographic f/stop; this means shorter exposure times. For example, a telescope with an 80mm clear aperture and a 480mm focal length is an f/6 optical system; a telescope with an 80mm clear aperture and an 800mm focal length is an f/10 optical system.Short focal length refractors and Newtonian reflectors are easier to store, transport and set-up than their longer focal length counterparts. Short focal length telescopes benefit from an increased field of view. With the excellent color correction of the APO refractor (or any reflector), one of the advantages of long focal length, minimizing chromatic aberration, is obviated.An optician I'm not, but it seems to me that the other advantage of long focal length is less chance of coma and other aberrations when using shallower curves in refractor lens cross section (or reflector primary mirrors -Editor), resulting in a sharper image. Using my short focal length Stellarvue SV80ST APO refractor (80mm aperture, 480mm focal length, f/6) for comparison, my eye cannot perceive any problem there. I have seen more such problems in some oculars than in my scope.It seems to me that the only other concern (regarding short focal length) is magnification limits due to the ratio of focal lengths of objective to ocular. I have another scope of greater aperture and focal length for when I want those advantages, but there are times when I really like the wide field and pinpoint stars shown by my short focal length SV80ST. Examples of that are the views of the Double Cluster and the Pleiades. Obviously, the SV80ST will show less lunar and planetary detail than a larger scope of equal quality, but once again, the APO's sharpness and contrast make for rewarding viewing. At star parties, where I can quickly compare views with club members' Dobs, I am still pleased with the SV80ST. In short, some of the disadvantages of short focal length can be overcome with technology and quality.Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

Zinc selenide (ZnSe) is another common material that is used in both visible and IR (MWIR & LWIR) from 0.45 to 21μm.  It is a light-yellow solid compound comprised of zinc and selenium. It is very similar to zinc sulfide, but has a slightly higher refractive index and is structurally weaker

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For a given clear aperture, a shorter focal length results in a larger photographic f/stop; this means shorter exposure times. For example, a telescope with an 80mm clear aperture and a 480mm focal length is an f/6 optical system; a telescope with an 80mm clear aperture and an 800mm focal length is an f/10 optical system.Short focal length refractors and Newtonian reflectors are easier to store, transport and set-up than their longer focal length counterparts. Short focal length telescopes benefit from an increased field of view. With the excellent color correction of the APO refractor (or any reflector), one of the advantages of long focal length, minimizing chromatic aberration, is obviated.An optician I'm not, but it seems to me that the other advantage of long focal length is less chance of coma and other aberrations when using shallower curves in refractor lens cross section (or reflector primary mirrors -Editor), resulting in a sharper image. Using my short focal length Stellarvue SV80ST APO refractor (80mm aperture, 480mm focal length, f/6) for comparison, my eye cannot perceive any problem there. I have seen more such problems in some oculars than in my scope.It seems to me that the only other concern (regarding short focal length) is magnification limits due to the ratio of focal lengths of objective to ocular. I have another scope of greater aperture and focal length for when I want those advantages, but there are times when I really like the wide field and pinpoint stars shown by my short focal length SV80ST. Examples of that are the views of the Double Cluster and the Pleiades. Obviously, the SV80ST will show less lunar and planetary detail than a larger scope of equal quality, but once again, the APO's sharpness and contrast make for rewarding viewing. At star parties, where I can quickly compare views with club members' Dobs, I am still pleased with the SV80ST. In short, some of the disadvantages of short focal length can be overcome with technology and quality.Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

Calcium fluoride (CaF2) optics are ideal for a broad range of Ultraviolet (UV), Visible, or Infrared (IR) applications. Its low refractive index reduces the need for anti-reflective coatings. Its application ranges from thermal imaging systems to excimer lasers making it a very versatile material for ultraviolet (UV) to infrared (IR) frequencies.

20141126 — The wave-plate, or circular, polarization concept would enable laser-beam polarization smoothing even without cross-beam energy transfer. In ...

Argument in favor of SHORTER (f/5-f/7) focal length telescopes (by Gordon Landers)For a given clear aperture, a shorter focal length results in a larger photographic f/stop; this means shorter exposure times. For example, a telescope with an 80mm clear aperture and a 480mm focal length is an f/6 optical system; a telescope with an 80mm clear aperture and an 800mm focal length is an f/10 optical system.Short focal length refractors and Newtonian reflectors are easier to store, transport and set-up than their longer focal length counterparts. Short focal length telescopes benefit from an increased field of view. With the excellent color correction of the APO refractor (or any reflector), one of the advantages of long focal length, minimizing chromatic aberration, is obviated.An optician I'm not, but it seems to me that the other advantage of long focal length is less chance of coma and other aberrations when using shallower curves in refractor lens cross section (or reflector primary mirrors -Editor), resulting in a sharper image. Using my short focal length Stellarvue SV80ST APO refractor (80mm aperture, 480mm focal length, f/6) for comparison, my eye cannot perceive any problem there. I have seen more such problems in some oculars than in my scope.It seems to me that the only other concern (regarding short focal length) is magnification limits due to the ratio of focal lengths of objective to ocular. I have another scope of greater aperture and focal length for when I want those advantages, but there are times when I really like the wide field and pinpoint stars shown by my short focal length SV80ST. Examples of that are the views of the Double Cluster and the Pleiades. Obviously, the SV80ST will show less lunar and planetary detail than a larger scope of equal quality, but once again, the APO's sharpness and contrast make for rewarding viewing. At star parties, where I can quickly compare views with club members' Dobs, I am still pleased with the SV80ST. In short, some of the disadvantages of short focal length can be overcome with technology and quality.Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

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Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

Since focal length is a linear measurement of the scope's light path, conventional refractors and Newtonian reflectors must be physically at least as long as their focal length. Catadioptric (CAT) telescopes fold the light path back and forth internally and thus are typically much shorter, physically, than their optical focal length. This makes for a relatively short, compact optical tube and gives CAT's a big advantage in portability.The focal length of any telescope (or other lens system) determines its angular field of view. A longer focal length telescope takes in a narrower field of view and a shorter focal length scope takes in a wider field of view. This is easily demonstrated by taking photos through two telescopes of different focal length from the same position with cameras attached directly to the back of their optical tubes at the point of focus. This is called prime focal length photography and the photo from the shorter focal length scope will show a wider field of view, regardless of the aperture or design of the telescopes. In other words, it is focal length that determines a telescope's field of view, regardless of the diameter of the objective lens or primary mirror.Viewing through an eyepiece is more complicated, because the eyepiece is also a lens system with a focal length that interacts with the prime focal length of the telescope. The focal length of the telescope divided by the focal length of the eyepiece determines the magnification you see. Given eyepieces designed with the same apparent field of view (AFOV), a shorter focal length eyepiece will give a smaller field of view (and greater magnification) in any given telescope.Argument in favor of SHORTER (f/5-f/7) focal length telescopes (by Gordon Landers)For a given clear aperture, a shorter focal length results in a larger photographic f/stop; this means shorter exposure times. For example, a telescope with an 80mm clear aperture and a 480mm focal length is an f/6 optical system; a telescope with an 80mm clear aperture and an 800mm focal length is an f/10 optical system.Short focal length refractors and Newtonian reflectors are easier to store, transport and set-up than their longer focal length counterparts. Short focal length telescopes benefit from an increased field of view. With the excellent color correction of the APO refractor (or any reflector), one of the advantages of long focal length, minimizing chromatic aberration, is obviated.An optician I'm not, but it seems to me that the other advantage of long focal length is less chance of coma and other aberrations when using shallower curves in refractor lens cross section (or reflector primary mirrors -Editor), resulting in a sharper image. Using my short focal length Stellarvue SV80ST APO refractor (80mm aperture, 480mm focal length, f/6) for comparison, my eye cannot perceive any problem there. I have seen more such problems in some oculars than in my scope.It seems to me that the only other concern (regarding short focal length) is magnification limits due to the ratio of focal lengths of objective to ocular. I have another scope of greater aperture and focal length for when I want those advantages, but there are times when I really like the wide field and pinpoint stars shown by my short focal length SV80ST. Examples of that are the views of the Double Cluster and the Pleiades. Obviously, the SV80ST will show less lunar and planetary detail than a larger scope of equal quality, but once again, the APO's sharpness and contrast make for rewarding viewing. At star parties, where I can quickly compare views with club members' Dobs, I am still pleased with the SV80ST. In short, some of the disadvantages of short focal length can be overcome with technology and quality.Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

Custom IR windows are popular because they allow for the transmission of infrared light while providing protection to sensitive infrared sensors and systems. IR windows, stepped windows, lenses, and other precision optics made from materials such as calcium fluoride, germanium, magnesium fluoride, sapphire, silicon, zinc selenide and zinc sulfide, which are highly transparent in the infrared spectrum and possess excellent durability and thermal stability. IR precision optics are ideal for a range of applications, including thermal imaging, spectroscopy, and environmental monitoring. Their ability to withstand harsh environments while maintaining high optical performance ensures accurate and reliable measurements in various industrial, military, and scientific settings.

What istransparentto infrared light

Sapphire crystal (Al2O3) is an optimal choice due to its mechanical strength, scratch resistance, and its hardness which is second only to diamond. It is used in ultraviolet (UV) and visible wavelengths beginning around 150nm and also performs well in IR to around 5µm. The downside to sapphire is the high material and processing costs.

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An optician I'm not, but it seems to me that the other advantage of long focal length is less chance of coma and other aberrations when using shallower curves in refractor lens cross section (or reflector primary mirrors -Editor), resulting in a sharper image. Using my short focal length Stellarvue SV80ST APO refractor (80mm aperture, 480mm focal length, f/6) for comparison, my eye cannot perceive any problem there. I have seen more such problems in some oculars than in my scope.It seems to me that the only other concern (regarding short focal length) is magnification limits due to the ratio of focal lengths of objective to ocular. I have another scope of greater aperture and focal length for when I want those advantages, but there are times when I really like the wide field and pinpoint stars shown by my short focal length SV80ST. Examples of that are the views of the Double Cluster and the Pleiades. Obviously, the SV80ST will show less lunar and planetary detail than a larger scope of equal quality, but once again, the APO's sharpness and contrast make for rewarding viewing. At star parties, where I can quickly compare views with club members' Dobs, I am still pleased with the SV80ST. In short, some of the disadvantages of short focal length can be overcome with technology and quality.Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

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Infrared plastic

In conclusion, there are many material options available for infrared capabilities and whether you need a IR windows, lenses, or freeform optics, we are available to help you find solutions to your objectives. Our manufacturing team can fabricate windows, prisms, lenses, aspherical lenses, and prototypes all in-house. Please reach out to us on your next project today at sales@EscoOptics.com.

There is another group of materials that perform well in the IR but require a high amount of safety precautions during manufacturing due to their harmful material makeup. Chalcogenide glass is a glass containing one or more chalcogens (sulfur, selenium and tellurium, but excluding oxygen). Such glasses are covalently bonded materials and may be classified as covalent network solids. Chalcogenide glass remains amorphous while exhibiting optical transparency over the full IR region of 2-20µm.

Is silicontransparentto infrared

Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

Gymax 4 PCS Bed Wedge Pillow Incline Head Support Rest Memory Foam Blue.

Magnesium fluoride (MgF2) is also a crystalline material that transmits well from the UV through the MWIR spectral bands (0.1 to 7.0μm). Magnesium Fluoride has relatively low cost; however, is thermally sensitive and requires special handling considerations.

NIR and SWIR together are sometimes called "reflected infrared", whereas MWIR and LWIR are sometimes referred to as "thermal infrared".

IR fused silica is virtually free of OH-ions providing superior transmittance at the 2.7μm wavelength “water band” region where standard UV grade fused silica absorbs light. The low OH content (<1 ppm) expands the overall usable range of fused silica to 3.6 microns. As with other fused silica designations, IR grade also shares the same outstanding homogeneity, bubble characteristics, low coefficient of thermal expansion, and chemical resistance.

IRabsorbing material

Silicon (Si) is a crystalline material like germanium primarily used within consumer electronics for microchips, as well as, extensive use in the semiconductor industry. Silicon is an excellent choice for windows and lenses in the 3μm to 5μm MWIR spectral bands for use in imaging, biomedical and military applications. Silicon optics are more heat resistant than germanium ones, as operating germanium in temperatures higher than 100°C leads to reduced optical properties.

Focal length, the specification of concern in this article, is defined as the distance from the optical center of a lens (or optical system) to its point of focus when focused at infinity. (See the diagram of a simple lens at the top of this page.) The optical center of a multi-element lens system, like a camera lens, is defined as the "rear nodal point" and usually does not coincide exactly with the physical center of the lens system. As applied to telescopes, this definition works perfectly for refractors, since they use lenses to focus light. The focal length of reflector telescopes, which use mirrors instead of lenses, is measured from the first active optical element (the corrector in an SCT or the surface of the primary mirror in a Newtonian) to the point of focus.Since focal length is a linear measurement of the scope's light path, conventional refractors and Newtonian reflectors must be physically at least as long as their focal length. Catadioptric (CAT) telescopes fold the light path back and forth internally and thus are typically much shorter, physically, than their optical focal length. This makes for a relatively short, compact optical tube and gives CAT's a big advantage in portability.The focal length of any telescope (or other lens system) determines its angular field of view. A longer focal length telescope takes in a narrower field of view and a shorter focal length scope takes in a wider field of view. This is easily demonstrated by taking photos through two telescopes of different focal length from the same position with cameras attached directly to the back of their optical tubes at the point of focus. This is called prime focal length photography and the photo from the shorter focal length scope will show a wider field of view, regardless of the aperture or design of the telescopes. In other words, it is focal length that determines a telescope's field of view, regardless of the diameter of the objective lens or primary mirror.Viewing through an eyepiece is more complicated, because the eyepiece is also a lens system with a focal length that interacts with the prime focal length of the telescope. The focal length of the telescope divided by the focal length of the eyepiece determines the magnification you see. Given eyepieces designed with the same apparent field of view (AFOV), a shorter focal length eyepiece will give a smaller field of view (and greater magnification) in any given telescope.Argument in favor of SHORTER (f/5-f/7) focal length telescopes (by Gordon Landers)For a given clear aperture, a shorter focal length results in a larger photographic f/stop; this means shorter exposure times. For example, a telescope with an 80mm clear aperture and a 480mm focal length is an f/6 optical system; a telescope with an 80mm clear aperture and an 800mm focal length is an f/10 optical system.Short focal length refractors and Newtonian reflectors are easier to store, transport and set-up than their longer focal length counterparts. Short focal length telescopes benefit from an increased field of view. With the excellent color correction of the APO refractor (or any reflector), one of the advantages of long focal length, minimizing chromatic aberration, is obviated.An optician I'm not, but it seems to me that the other advantage of long focal length is less chance of coma and other aberrations when using shallower curves in refractor lens cross section (or reflector primary mirrors -Editor), resulting in a sharper image. Using my short focal length Stellarvue SV80ST APO refractor (80mm aperture, 480mm focal length, f/6) for comparison, my eye cannot perceive any problem there. I have seen more such problems in some oculars than in my scope.It seems to me that the only other concern (regarding short focal length) is magnification limits due to the ratio of focal lengths of objective to ocular. I have another scope of greater aperture and focal length for when I want those advantages, but there are times when I really like the wide field and pinpoint stars shown by my short focal length SV80ST. Examples of that are the views of the Double Cluster and the Pleiades. Obviously, the SV80ST will show less lunar and planetary detail than a larger scope of equal quality, but once again, the APO's sharpness and contrast make for rewarding viewing. At star parties, where I can quickly compare views with club members' Dobs, I am still pleased with the SV80ST. In short, some of the disadvantages of short focal length can be overcome with technology and quality.Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

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In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

It seems to me that the only other concern (regarding short focal length) is magnification limits due to the ratio of focal lengths of objective to ocular. I have another scope of greater aperture and focal length for when I want those advantages, but there are times when I really like the wide field and pinpoint stars shown by my short focal length SV80ST. Examples of that are the views of the Double Cluster and the Pleiades. Obviously, the SV80ST will show less lunar and planetary detail than a larger scope of equal quality, but once again, the APO's sharpness and contrast make for rewarding viewing. At star parties, where I can quickly compare views with club members' Dobs, I am still pleased with the SV80ST. In short, some of the disadvantages of short focal length can be overcome with technology and quality.Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

A comparison of dual-galvonometer lasers and flatbed laser systems and how they are used to mark parts, tags, and other products.

Infraredtransparent materialschart

Zinc sulfide (ZnS) performs best between 8 to 12µm region. Although a lower cost relative to ZnSe, it does not have the longer transmission range. As a strong and stable material, ZnSe has high resistance to particulate abrasion making it an ideal solution for IR windows on aircraft platforms.

Germanium (Ge) is a grayish non-transparent crystalline material and one of the most commonly used infrared materials. It is an optimal material for night vision and thermal imaging systems in the MWIR and the LWIR band. Germanium transmission performs best between 8 and 12µm. Ge has a low optical dispersion and a high refractive index which makes it an ideal solution for a wider field of view lenses. Its crystal structure is similar to diamond and when a DLC coating is applied (Diamond Like Carbon), it becomes very durable against outdoor elements and harsh environments.

The "Fresnel Equations". Brewster's Angle. Total internal reflection. Power reflectance and transmittance. Augustin Fresnel. 1788-1827. Page 2. Posing the ...

When dealing with the infrared region, it is important to know this part of the electromagnetic spectrum breaks down into further sub-sections.

A longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

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The focal length of any telescope (or other lens system) determines its angular field of view. A longer focal length telescope takes in a narrower field of view and a shorter focal length scope takes in a wider field of view. This is easily demonstrated by taking photos through two telescopes of different focal length from the same position with cameras attached directly to the back of their optical tubes at the point of focus. This is called prime focal length photography and the photo from the shorter focal length scope will show a wider field of view, regardless of the aperture or design of the telescopes. In other words, it is focal length that determines a telescope's field of view, regardless of the diameter of the objective lens or primary mirror.Viewing through an eyepiece is more complicated, because the eyepiece is also a lens system with a focal length that interacts with the prime focal length of the telescope. The focal length of the telescope divided by the focal length of the eyepiece determines the magnification you see. Given eyepieces designed with the same apparent field of view (AFOV), a shorter focal length eyepiece will give a smaller field of view (and greater magnification) in any given telescope.Argument in favor of SHORTER (f/5-f/7) focal length telescopes (by Gordon Landers)For a given clear aperture, a shorter focal length results in a larger photographic f/stop; this means shorter exposure times. For example, a telescope with an 80mm clear aperture and a 480mm focal length is an f/6 optical system; a telescope with an 80mm clear aperture and an 800mm focal length is an f/10 optical system.Short focal length refractors and Newtonian reflectors are easier to store, transport and set-up than their longer focal length counterparts. Short focal length telescopes benefit from an increased field of view. With the excellent color correction of the APO refractor (or any reflector), one of the advantages of long focal length, minimizing chromatic aberration, is obviated.An optician I'm not, but it seems to me that the other advantage of long focal length is less chance of coma and other aberrations when using shallower curves in refractor lens cross section (or reflector primary mirrors -Editor), resulting in a sharper image. Using my short focal length Stellarvue SV80ST APO refractor (80mm aperture, 480mm focal length, f/6) for comparison, my eye cannot perceive any problem there. I have seen more such problems in some oculars than in my scope.It seems to me that the only other concern (regarding short focal length) is magnification limits due to the ratio of focal lengths of objective to ocular. I have another scope of greater aperture and focal length for when I want those advantages, but there are times when I really like the wide field and pinpoint stars shown by my short focal length SV80ST. Examples of that are the views of the Double Cluster and the Pleiades. Obviously, the SV80ST will show less lunar and planetary detail than a larger scope of equal quality, but once again, the APO's sharpness and contrast make for rewarding viewing. At star parties, where I can quickly compare views with club members' Dobs, I am still pleased with the SV80ST. In short, some of the disadvantages of short focal length can be overcome with technology and quality.Argument in favor of LONGER (f/9-f/11) focal length telescopes (by Chuck Hawks)Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil).It is difficult to manufacture the more radical lens shapes required by short focal length refractors; they also typically require more expensive (ED) glasses. The price of such telescopes must consequently be higher or their optical performance will suffer. In catadioptric telescopes and reflectors, shorter focal length for any given aperture results in a proportionally larger central obstruction, which degrades contrast and overall optical quality.Longer focal length gives you greater magnification with any given eyepiece. This means more magnification from your shortest focal length eyepiece. For the same magnification, you can use a longer focal length eyepiece, and longer eyepieces are generally better and easier to look through than shorter ones. This is particularly important for astronomers relying mainly on (comparatively affordable) Plossl eyepieces, which use four lens elements in two groups. In the longer focal lengths (about 25mm and up), such eyepieces have good eye relief and good sized ocular lenses. Unfortunately, their eye relief rapidly decreases with focal length, as does the diameter of the eyepiece's ocular lens. With Plossl eyepieces of short focal length, it is as if you are peering through a pinhole. Eyepieces of advanced design using ED glasses and six (or more) elements (Tele Vue Radians and Naglers, for example) can overcome these drawbacks, but cost much more than Plossls.In my opinion, the ocular is often the weakest link in the viewing system. The shorter the ocular, the more exotic, expensive and (usually) physically larger it must be to function adequately. For example, when A&P Online staff member Jim Fleck (Celestron C8, 2032mm focal length) and I (Stellarvue SV115T, 800mm focal length) were comparing views of Jupiter through our telescopes, I had to use a 7mm eyepiece (114x) to approximate the image size he was getting with an 18mm eyepiece (113x). To me, that gave his scope one heck of a built-in viewing advantage. That is why I prefer the longer focal length that accompanies a medium focal ratio of about f/9-f/11, instead of the f/5-f/7 focal ratios so common today in APO refractors and Dobsonian Newtonians.Summary - Benefits of short focal lengthShorter focal length allows a physically shorter telescope. Shorter focal length means a wider angular field of view at prime focal length or with any given eyepiece. For a given clear aperture, a shorter focal length results in a larger ("faster") photographic f/stop.Summary - Benefits of long focal lengthA longer focal length eases optical design and manufacturing problems, permitting a telescope with superior optical performance and/or a lower price. Longer focal length allows higher magnification at prime focal length and with any given eyepiece. Allows use of a longer focal length ocular to achieve a given visual image size (magnification).

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