Collimator-AI

The transition area, or edge, is available in different variations (soft, hard, attenuator). The most common is a soft edge and provides a smooth transition from the ND side and the clear side. Hard-edge filters have a sharp transition from ND to clear, and the attenuator edge changes gradually over most of the filter, so the transition is less noticeable.

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One main disadvantage of neutral-density (ND) filters is that different shooting situations often require a variety of filters, which can become quite expensive. For example, using screw-on filters requires a separate set for each lens diameter, though inexpensive step-up rings can minimize this requirement.

By J. Guthrie A collimator is a simple device that uses a reflective surface and lenses to replicate a target at infinity.

I carry a lot of gear to the shooting range, so much, in fact, that I have to requisition my parent's minivan just to carry it all. Some of it is snivel gear, some of it superfluous, but there are a few items I simply cannot live without. A collimator is one of those have-to-have items for me, or any other shooter who likes to save time, trouble, and ammunition.

Large telescopes can cause the Moon and planets to become too bright and lose contrast. A neutral-density filter can increase the contrast and cut down the brightness, making these objects easier to view.

A graduated ND filter is similar, except that the intensity varies across the surface of the filter. This is useful when one region of the image is bright and the rest is not, as in a picture of a sunset.

I carry a lot of gear to the shooting range, so much, in fact, that I have to requisition my parent's minivan just to carry it all. Some of it is snivel gear, some of it superfluous, but there are a few items I simply cannot live without. A collimator is one of those have-to-have items for me, or any other shooter who likes to save time, trouble, and ammunition.

For an ND filter with optical density d, the fraction of the optical power transmitted through the filter can be calculated as

Do not forget to toss a collimator or bore-sighting device in your luggage before the next big hunting expedition. It can be a huge help if the baggage apes happen to drop your rifle case from a great height and knock the scope around. Before your trip, attach a collimator to the zeroed rifle and make a note of where the crosshairs fall on the grid. In fact, make a note card and put it in your rifle case. Once in camp, attach the collimator and cross-check it with your notes. If the scope has been jarred off zero, that should be indicated on the grid. Move the reticle back to the correct position and fire a few shots to confirm your zero. Laser devices can obviously be used the same way, just be sure your marked target is exactly the same distance in camp as it was on the range.

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For example, one might wish to photograph a waterfall at a slow shutter speed to create a deliberate motion-blur effect. The photographer might determine that to obtain the desired effect, a shutter speed of ten seconds was needed. On a very bright day, there might be so much light that even at minimal film speed and a minimal aperture, the ten-second shutter speed would let in too much light, and the photo would be overexposed. In this situation, applying an appropriate neutral-density filter is the equivalent of stopping down one or more additional stops, allowing the slower shutter speed and the desired motion-blur effect.

Collimatorsight

Most collimators use an expanding or caliber-specific arbor--I've also heard it called a spud--that fits snuggly into the bore and onto which the collimator is affixed. Looking through the scope, a grid or reticle should greet the eye. It is just a matter of adjusting the windage and elevation so the scope's reticle aligns with the collimator's reticle or the center of the grid. The scope and the bore are then aligned, but keep in mind that the two axes are parallel or converge at some point that may or may not coincide with the bullet's trajectory exactly where needed. Quite a few factors, including the scope's height above the bore and miniscule alignment errors, prevent the bore sighting from being perfect every time.

You will, absolutely, positively, have to fine-tune the rifle so that the reticle and bullet's point of impact are at the same place. Working behind the gun counter at several gun stores, I always took a few minutes to bore sight a customer's rifle/scope combo and was amazed by the number of people who thought the gun was ready for the field. The aforementioned factors and the error induced by the shooter usually account for a couple of inches at 100 yards. My rifles are usually within 3 or so inches, but never have I been perfectly zeroed after bore sighting.

There are other solutions to the problem, most notably centering a laser-emitting device in the bore and moving the scope's reticle to the laser's point of impact on a distant target. Some companies use dummy cartridges, others use an arbor with an attached laser. I have used both and found them to be very handy, but the system still must be double-checked like a collimator. The only downside is the necessity of a downrange target--most require at least 25 yards--and picking up the laser. That can be tough on bright, sunny days. Recommended Advertisement

Collimatorin radiology

ND filters find applications in several high-precision laser experiments because the power of a laser cannot be adjusted without changing other properties of the laser light (e.g. collimation of the beam). Moreover, most lasers have a minimal power setting at which they can be operated. To achieve the desired light attenuation, one or more neutral-density filters can be placed in the path of the beam.

In photography and optics, a neutral-density filter, or ND filter, is a filter that reduces or modifies the intensity of all wavelengths, or colors, of light equally, giving no changes in hue of color rendition. It can be a colorless (clear) or grey filter, and is denoted by Wratten number 96. The purpose of a standard photographic neutral-density filter is to reduce the amount of light entering the lens. Doing so allows the photographer to select combinations of aperture, exposure time and sensor sensitivity that would otherwise produce overexposed pictures. This is done to achieve effects such as a shallower depth of field or motion blur of a subject in a wider range of situations and atmospheric conditions.

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Collimatorin spectrometer

Most collimators use an expanding or caliber-specific arbor--I've also heard it called a spud--that fits snuggly into the bore and onto which the collimator is affixed. Looking through the scope, a grid or reticle should greet the eye. It is just a matter of adjusting the windage and elevation so the scope's reticle aligns with the collimator's reticle or the center of the grid. The scope and the bore are then aligned, but keep in mind that the two axes are parallel or converge at some point that may or may not coincide with the bullet's trajectory exactly where needed. Quite a few factors, including the scope's height above the bore and miniscule alignment errors, prevent the bore sighting from being perfect every time.

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Collimators and laser bore-sighting devices are relatively inexpensive. Caliber-specific cartridges usually run $50 to $70, and multi-caliber kits go for $40 on up. Leupold makes a pretty cool magnetic collimator that works on most every barrel; it runs $70. With premium ammo running $40 or $50 a box, it is pretty easy to see how a collimator can pay for itself in just a few range sessions. And on top of that, it will save some time and a little bit of your sanity.

Collimatorgun

The advantage of this approach is reduced bulk and expenses, but one drawback is a loss of image quality caused by both using two elements together and by combining two polarizing filters.

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The use of an ND filter allows the photographer to use a larger aperture that is at or below the diffraction limit, which varies depending on the size of the sensory medium (film or digital) and for many cameras is between f/8 and f/11, with smaller sensory medium sizes needing larger-sized apertures, and larger ones able to use smaller apertures. ND filters can also be used to reduce the depth of field of an image (by allowing the use of a larger aperture) where otherwise not possible due to a maximal shutter speed limit.

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Collimatorlens

Do not forget to toss a collimator or bore-sighting device in your luggage before the next big hunting expedition. It can be a huge help if the baggage apes happen to drop your rifle case from a great height and knock the scope around. Before your trip, attach a collimator to the zeroed rifle and make a note of where the crosshairs fall on the grid. In fact, make a note card and put it in your rifle case. Once in camp, attach the collimator and cross-check it with your notes. If the scope has been jarred off zero, that should be indicated on the grid. Move the reticle back to the correct position and fire a few shots to confirm your zero. Laser devices can obviously be used the same way, just be sure your marked target is exactly the same distance in camp as it was on the range.

In practice, ND filters are not perfect, as they do not reduce the intensity of all wavelengths equally. This can sometimes create color casts in recorded images, particularly with inexpensive filters. More significantly, most ND filters are only specified over the visible region of the spectrum and do not proportionally block all wavelengths of ultraviolet or infrared radiation. This can be dangerous if using ND filters to view sources (such as the Sun or white-hot metal or glass), which emit intense invisible radiation, since the eye may be damaged even though the source does not look bright when viewed through the filter. Special filters must be used if such sources are to be safely viewed.

To address this issue, some manufacturers have developed variable ND filters. These filters consist of two polarizing filters, with at least one being rotatable. The rear filter blocks light in one plane, while the front filter can be adjusted. As the front filter rotates, it cuts down the amount of light reaching the camera sensor, allowing for nearly infinite control over light levels.

A collimator does not require a trip downrange, which is nice when the firing line is full and you have to time your trips downrange with everyone else. Both collimators and arbor/cartridge-mounted lasers are more accurate than the old tried-and-true method of peering down the bore, and they work on action types that do not allow a clear line of sight down the barrel.

There are other solutions to the problem, most notably centering a laser-emitting device in the bore and moving the scope's reticle to the laser's point of impact on a distant target. Some companies use dummy cartridges, others use an arbor with an attached laser. I have used both and found them to be very handy, but the system still must be double-checked like a collimator. The only downside is the necessity of a downrange target--most require at least 25 yards--and picking up the laser. That can be tough on bright, sunny days.

Ever fire a 100-yard sighting shot at an 11x17-inch target and completely miss it? We probably all have. After that, we're reduced to firing at the left edge, right edge, top, and bottom until we get a shot on paper in order to adjust the scope. The thought of wasting precious ammo keeps me up at night, and a collimator will get that first shot close to center almost every time. It also saves you the agony of trying to pick out the most recent bullet hole from the thousands of other holes in the target board around the just-missed target. Advertisement ×

There are all kinds of collimators, which, by definition, is a device that narrows a beam of particles or waves. Oncologists use them to focus radiation waves onto cancer cells; industry uses collimators to focus lasers. When applied to the shooting world, collimators use a bit of optical trickery to replicate a distant target without introducing parallax to the equation. The device allows one to calibrate a riflescope so it is aligned with the axis of the bore. In short, a collimator creates a target 100 yards away using just the length of a rifle barrel, a reflective surface, and a few lenses, and it gets the scope and barrel pointed in the same direction without ever firing a shot.

Ever fire a 100-yard sighting shot at an 11x17-inch target and completely miss it? We probably all have. After that, we're reduced to firing at the left edge, right edge, top, and bottom until we get a shot on paper in order to adjust the scope. The thought of wasting precious ammo keeps me up at night, and a collimator will get that first shot close to center almost every time. It also saves you the agony of trying to pick out the most recent bullet hole from the thousands of other holes in the target board around the just-missed target.

In photography, ND filters are quantified by their optical density or equivalently their f-stop reduction. In microscopy, the transmittance value is sometimes used. In astronomy, the fractional transmittance is sometimes used (eclipses).

Collimators and laser bore-sighting devices are relatively inexpensive. Caliber-specific cartridges usually run $50 to $70, and multi-caliber kits go for $40 on up. Leupold makes a pretty cool magnetic collimator that works on most every barrel; it runs $70. With premium ammo running $40 or $50 a box, it is pretty easy to see how a collimator can pay for itself in just a few range sessions. And on top of that, it will save some time and a little bit of your sanity.

Another type of ND filter configuration is the ND-filter wheel. It consists of two perforated glass disks that have progressively denser coating applied around the perforation on the face of each disk. When the two disks are counter-rotated in front of each other, they gradually and evenly go from 100% transmission to 0% transmission. These are used on catadioptric telescopes mentioned above and in any system that is required to work at 100% of its aperture (usually because the system is required to work at its maximal angular resolution).

CollimatorX ray

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You will, absolutely, positively, have to fine-tune the rifle so that the reticle and bullet's point of impact are at the same place. Working behind the gun counter at several gun stores, I always took a few minutes to bore sight a customer's rifle/scope combo and was amazed by the number of people who thought the gun was ready for the field. The aforementioned factors and the error induced by the shooter usually account for a couple of inches at 100 yards. My rifles are usually within 3 or so inches, but never have I been perfectly zeroed after bore sighting.

Instead of reducing the aperture to limit light, the photographer can add a ND filter to limit light, and can then set the shutter speed according to the particular motion desired (blur of water movement, for example) and the aperture set as needed (small aperture for maximal sharpness or large aperture for narrow depth of field (subject in focus and background out of focus)). Using a digital camera, the photographer can see the image right away and choose the best ND filter to use for the scene being captured by first knowing the best aperture to use for maximal sharpness desired. The shutter speed would be selected by finding the desired blur from subject movement. The camera would be set up for these in manual mode, and then the overall exposure adjusted darker by adjusting either aperture or shutter speed, noting the number of stops needed to bring the exposure to that which is desired. That offset would then be the amount of stops needed in the ND filter to use for that scene.

An inexpensive, homemade alternative to professional ND filters can be made from a piece of welder's glass. Depending on the rating of the welder's glass, this can have the effect of a 10-stop filter.

A collimator does not require a trip downrange, which is nice when the firing line is full and you have to time your trips downrange with everyone else. Both collimators and arbor/cartridge-mounted lasers are more accurate than the old tried-and-true method of peering down the bore, and they work on action types that do not allow a clear line of sight down the barrel.

collimatoris used for?

Neutral-density filters are used to control exposure with photographic catadioptric lenses, since the use of a traditional iris diaphragm increases the ratio of the central obstruction found in those systems, leading to poor performance.

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There are all kinds of collimators, which, by definition, is a device that narrows a beam of particles or waves. Oncologists use them to focus radiation waves onto cancer cells; industry uses collimators to focus lasers. When applied to the shooting world, collimators use a bit of optical trickery to replicate a distant target without introducing parallax to the equation. The device allows one to calibrate a riflescope so it is aligned with the axis of the bore. In short, a collimator creates a target 100 yards away using just the length of a rifle barrel, a reflective surface, and a few lenses, and it gets the scope and barrel pointed in the same direction without ever firing a shot.

To create ethereal looking landscapes and seascapes with extremely blurred water or other motion, the use of multiple stacked ND filters might be required. This has, as in the case of variable NDs, the effect of reducing image quality. To counter this, some manufacturers have produced high-quality extreme ND filters. Typically these are rated at a 10-stop reduction, allowing very slow shutter speeds even in relatively bright conditions.

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