Materials That Absorb Infrared Rays - materials transparent to ir

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The light-gathering ability of a microscope objective is quantitatively expressed in terms of the numerical aperture, which is a measure of the number of ...

Polarization examples

Selective advantage – A characteristic that gives an organism an advantage to its chance of surviving and reproducing. Over many generations this is likely to increase the chance of this being passed onto its descendants.

i would say it is more of personal preference really. Some like vulcano tops,some flat tops.Circle t`s came as vulcanos,Meade Rg`s same,Zeiss Zao 1 and 2,BGO,Astrotech,UO as flat tops.UO(university optics)where also made as vulcano tops.There where quite a few other orthos made under different brand names,like Antares,Celestron,Vixen etc.Orthos where and i think still are very popular for planetary observers.

The "volcano top" orthos used to be on the used market for rather low prices at one point which made them somewhat of a bargain. Their prices seem to have crept back up to closer to the more recent flat top designs now they are out of production.

I was just saying that I feel 40-50 deg quite claustrophobic and therefore I feel that I would not appreciate them. Hence I prefer not to buy even the most affordable ones, the bco'. This is because I am not interested in having a large collection of tools, but just using a lot what I already have. This is a personal opinion and doesn't have anything to do with excellent eyepieces out there.

Polarizationof light notes PDF

Don't be fooled by the price of the BCO Piero, the glass in these things are superb as are the coatings. They give black and green more than a run for their money IMHO.... Sorry for the "heresy"

We can see that for the focal ratio, Monocentric has best on-axis sharpness, ortho comes second, thereafter come achromat pair and könig.

As for the Pentax XO 5mm mentioned earlier.I do have one,it does deliver what it says on the tin and i have had some breath taking views with it,but as always there is a spoon of sand in this case its the eye relief of the Pentax XO. 3.8mm for 5 mm ortho is really tight.If you can live with that,you will be rewarded with some cracking views and i would love to see Pentax XO as a proper series of orthos and not only in 2 focal length`s. Would be prepared to pay the high price they demand,but this isnt going to happen sadly.

There are a few ortho's now on the market. I think they may be coming back into fashion. Talking of Celestron ortho's, I've never seen one, but I found this online:

Polarisation is a fascinating property of the electromagnetic spectrum. Let us take a whistle-stop tour of how polarisation is used in nature, some existing technologies that rely upon it, and how it may play a significant part in creating a guaranteed-private internet, secured by the laws of physics.

Intensity – The intensity of light can be measured in a number of ways, but one method is to measure the power over a given area, so is often measured in Wm-2.

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We can see that for the focal ratio, Monocentric has best on-axis sharpness, ortho comes second, thereafter come achromat pair and könig.

Linearpolarization

Yeah, I really find Plossls less than 8mm hard work, I should imagine ortho's are no easier even with possible better eye relief. I suppose anything rare that comes back into fashion will command high prices.

If the zebra did not deter the tabanid flies, it could have a negative consequence on its ability to survive and successfully reproduce, as the tabanids can be vectors of several pathogens, and when irritated the animals’ grazing can reduce, decreasing both milk production and body mass.

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I would like to think that Televue's claim are meant astigmatism suppression in the field (outer edge), especielly in faster scopes, since Televue has its patent in plossl design, USpatene4482217.

The y-axis (the MTF value) represents the contrast restitution for the corresponding spatial frequency. This value is between 0 and 100%, meaning complete ...

At school I loved an odd mix of subjects including science, maths and drama, and I spent a lot of free time biking and on my computer. Having dabbled in IT for a few years, I decided I missed talking to humans too much, so moved into teaching. These days I mainly teach teachers about physics, but I also get to discover and teach about new and interesting uses of science, including these quantum technologies. So far, teaching has taken to me Kazakhstan, Iraq, Canada, Iceland, Morocco and South Africa! I now have two young children, so I have much less free time, but I still like to spend some of it biking and on my computer.

Unsurprisingly, we humans look at the world around us with our peculiar human vision, and sometimes this limits our view of the world. Whilst it would be reasonable to assume that other creatures see the world in a similar way, this is not true. Indeed, our use of the phrase ‘visible light’, is also human-focussed; many animals’ eyes do not respond to the same part of the electromagnetic spectrum as human eyes do. Human eyes cover the portion 380 to 700 nanometers, using three types of cone with peak sensitivities corresponding to red, green and blue (unless you are colour-blind or perhaps even a tetrachromat). Some animals are sensitive to UV or infra-red, and many creatures have fewer or more than three types of colour-sensing cones. Some butterflies and mantis shrimps can detect up to 12 distinct wavelengths.

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Polarization waves real life examplesppt

Polarized and unpolarized light

There is also other information in the light all around us that is invisible to humans; which is that light can be polarised. Whilst our human eyes may be incapable, some creatures have evolved eyes that can detect the difference between light rays polarised along different axes. The reason zebras (and other animals) have stripes may be to reduce attacks from biting flies that can sense this polarisation.

Light, as created by the sun or by a normal light bulb, will be unpolarised: that is, all the rays of light will be polarised along different axes. However, light can be polarised (or partially polarised) when it reflects off a reflective surface, at a shallow angle.

I found that the "volcano top" shaped orthos made it easier to access the eye lens of the shorter focal lengths. Optically the more recent "flat top" Baader GO / Astro Hutech / Fujiyama orthos show slightly less light scatter and a little more transmission than the "volcano tops" to my eyes but the eye lens can be hard to locate and hold (for me at least) in 6mm focal lengths and below. My scopes are undriven though, which might not help with that !

by R Heintzmann · 2006 · Cited by 279 — Abbe's theory has to be modified if the emitted light can only be described by a nonlinear4 dependence of emission on the local excitation ...

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I don't understand why they lack popularity at times, the views they give are superb and the better the seeing gets the more they can pull away IMHO. I have no problem with a 5mm ortho in my truss dob , and the views are worth the nudging.

Don't be fooled by the price of the BCO Piero, the glass in these things are superb as are the coatings. They give black and green more than a run for their money IMHO.... Sorry for the "heresy"

Hi Gerry, I apologise, I should have clarified this better. I wasn't meaning that bco are cheap, likely not good. I know they are very very good, as one can read from your and other members' experiences.

What ispolarizationofwavesin Physics

I would like to think that Televue's claim are meant astigmatism suppression in the field (outer edge), especielly in faster scopes, since Televue has its patent in plossl design, USpatene4482217.

We can also polarise light by passing it through a polarising filter. By passing unpolarised light through a polarising filter half of the light will be absorbed by the filter, but the half that gets through will now be polarised to match that filter.

Digital cameras used USB-A on the computer end of the cable because it had nearly universal compatibility for many years.

Visible light – Only special because it is the part of the electromagnetic spectrum that humans (and some other mammals) can sense. It has a frequency of approximately 4×1018-8×1018 Hz and a corresponding wavelength of 740-380 nm.

Don't be fooled by the price of the BCO Piero, the glass in these things are superb as are the coatings. They give black and green more than a run for their money IMHO.... Sorry for the "heresy"

I honestly thought it was just advertising spiel by TeleVue. Although, the build quality of the eyepieces isn't in dispute. I thought a Plossl actually was an achromatic pair. I'm not that up on the history though. That link about optics is good though, I've bookmarked it. Thanks.

Electromagnetic spectrum – The full electromagnetic spectrum is often counted as radio waves, microwaves, infra-red, visible, ultraviolet, x-rays and gamma rays, but the distinction between these is usually associated with how they are used and/or how they are generated. Terahertz is an example which can be used for many non-destructive imaging purposes.

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No need to apologise Piero- they are cheap lol! and that is one of the beauties of them. I just wanted to emphasize the optical quality of these eyepieces. Orthos are definitely not for everyone and with the excellent widefields out there many don't see the need for them. BUT on nights of excellent seeing out they come or if we need to keep bright stars away from those cherished faint nebs...

You're in luck! They're on sale: http://www.firstlightoptics.com/japanese-made-eyepieces/hutech-orthoscopic-eyepiece.html

Discover more in The Peculiar Powers of Polarisation – in maths and in the quantum realm, where we look at its use in technology and the mathematics involved.

There isn't a huge difference between the 18mm AH ortho and the 20mm TV Plossl in overall size. The TV is a little bit more expensive (a few pounds Sterling) but you do get a rubber eye guard, a rubber barrel grip and a tapered barrel safety undercut.

The 20mm TV Plossl was one of my favourite eyepieces until it essentially got replaced by a 68° 19mm Panoptic. My 8mm, 11mm and 20mm TV Plossls don't really see that much use these days but I think Plossls are still relevant depending on what you are viewing. For low power views of open clusters or objects such as M42 I sometimes prefer a 25mm Plossl over the 24mm Panoptic. I think the 50° FOV can be limiting although a lot depends on field stop and eye lens size. Plossls can vary a bit with this which is generally why I use TeleVues.

On the other hand, Televue plossls are not true plossls (just as all the other nowadays' plossl), they're symetric doublet (achromat pair), and from the pictures in the middle of this page

Polarizationof electromagneticwavespdf

TeleVue claim: ‘Tele Vue Plössls deliver sharper images than any other brand of 4 or 5 element "Plossl" or Orthoscopic designs’ and though I don't deny their remarkable quality I couldn't detect any difference in sharpness between the Astro Hutech 18mm and the TeleVue 20mm.

To understand what polarisation is, we must first be comfortable with the idea that light is part of the electromagnetic spectrum, which travels as transverse waves. These waves are made up of electric fields and magnetic fields, oscillating in phase at 90° to each other. When we are drawing polarised light, to simplify the picture, we normally only draw the oscillating electric field.

many might not see the need of the "cheap" orthos,despite some of the orthos are not that cheap and actually can cost even more then Ethos,but in my opinion,if you are after some critical detail on planetary or even a DSO object and dont need to see those extra degrees of FOV,nothing can beat a good old ortho and that has been conformed by many observers many times over.

I think I've seen some of those. Some people prefer the volcano top with ortho's, although I suppose only the really short focal length ones really need it.

The USAF Test Target was developed for use with the U.S. Government specification Mil-Std-150. It is one of the most commonly used resolution targets.

On the other hand, Televue plossls are not true plossls (just as all the other nowadays' plossl), they're symetric doublet (achromat pair), and from the pictures in the middle of this page

Another example of polarisation in nature is when looking at the stripes of a zebra. Studies have shown that zebras are attacked less by tabanids (a biting horse-fly) than equivalent horses that are a solid colour, whether those horses were black, white, brown or grey. This is attributed to the coloured stripes on a zebra causing partial polarisation of the light in alternating directions, which can be viewed by camera using different filters. The studies demonstrate that putting alternating polarising stripes on a grey surface reduces the number of tabanids attracted, even though it would appear to a human as a totally homogenous, grey surface. They were also able to show that having these lines too close or too far apart reduced the effectiveness of this protection.

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In 1932, Dr Edwin Land produced the world’s first commercially available polarising filter, which he called the Polaroid. Since then, polarising filters have become relatively common place, with sunglasses and camera lenses using them to reduce reflections. 3D films send selective images to each eye using differently polarised lenses, and a liquid crystal display (LCD) uses liquid crystal molecules between two polarising sheets – the molecules align themselves when an electric current passes between them, causing some frequencies of light to become blocked.

I have a TV 20mm plossl which is a very good EP to me. I find 50 deg a bit claustrophobic though.. This is the reason why I don't go for the cheap bco. On the other hand, I'm a bit tempted due to the constant positive opinions by members.

Tetrachromats – Some humans have four cones in their eyes. Whilst they cover the same frequency ranges are the three cones, these additional cones give tetrachromats the chance to distinguish between more variations in colour than trichromats.

Examplesofpolarizationin society

Being able to sense the polarisation of light is surprisingly common in the animal kingdom. We know it is used by many arthropods (spiders, insects, crustaceans) and also cephalopods (squid, octopi) – where it is thought it may be used to improve vision in the absence of colour.

Where does the verb polarize come from? ... The earliest known use of the verb polarize is in the 1810s. OED's earliest evidence for polarize is from 1811, in ...

Bees are excellent navigators, and it is thought that their sensitivity to polarisation may play a significant factor. Whilst the light that comes from the sun is unpolarised, as it hits our atmosphere it is scattered (causing light to appear to come from everywhere in the sky, not just from the sun). As it is scattered, a portion of the light becomes polarised. Whilst the polarising effect in the atmosphere is small, it does mean that when we study a cloudless sky, the light will be slightly polarised in circles around the sun. This means that even if a bee can only see a tiny portion of a cloudless sky, it will still know what the direction of the sun is – therefore helping it to navigate, giving a polarising-sensitive bee a selective advantage.

Well there is nothing like an eyepiece contrast, Orthoscopic and Ethos, bit like chalk and cheese FOV wise. Having both I do like the wide field E's on the Dob for just the user friendlyness of them but orthos come into their own on the driven scopes with planets. In fact the only thing I am not over keen on is that tight ER on the 5mm, so I don't know what the 4mm will be like. I then only find this is time limiting as to how long you can use them.

Transverse waves – Transverse waves have oscillations that are perpendicular to the direction of the wave’s travel, for example electromagnetic waves, seismic S (secondary) waves and the vibrations on a guitar.

If you really are a fan of orthos and have the cash to burn and can get your hands on Pentax XO,get it and you will love it.it is truly a magnificent eye piece.

Yeah just about any uv light can be used. And that narrow 5nm doesn't mean anything, I assume that range is given for optimal curing I'm not ...

Colour-blind – Approximately 1-in-12 men and 1-in-200 women have some form of colour blindness – where one type of the colour cone cells is absent, or does not work as expected (dichromacy). Approximately 3-in-100 000 people are totally colour-blind and only see in shades of grey.