Spotting Scopes

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	Coated, fully-coated, multicoated, fully-multicoated optics. Why are these important? Optical coatings reduce internal light loss and glare and ensure even light transmission, resulting in greater image sharpness and contrast. Spotting scopes have numerous glass surfaces, each one contributing to scattered light, so coatings make a big difference in what you see. Coated optics will have a less shiny, even dark appearance when looking into the barrel or tube. You may see a greenish, bluish or brownish tint as well. Most coatings are magnesium fluoride or calcium fluoride and work by destructively interfering with certain colors or wavelengths of light, eliminating their reflection. More light gets into your scope and more light is able to pass through to your eyes. Almost all modern consumer optics have some kind of coating on most of the optical elements. However, there are different levels and qualities of coatings. Coated optics means that at least one of the major optical elements has a coating on at least one surface. Fully-coated means that all lenses and glass surfaces have a coating layer. Multicoated means that at least one of the major optical elements in a fully-coated scope has multiple coatings of antireflective compounds on at least one surface. Fully-multicoated means all glass surfaces have multiple coatings and it is the best kind, resulting in light transmission of 90-95 percent, bright, sharp and contrasty images.


	Tripods and spotting scope stability – what do I need to know? In order to take full advantage of the magnification of a spotting scope, you should use it with a tripod to stabilize your view. The tripod you use will mostly depend on the size, weight and focal length of the scope you have. Table-top tripods extend 6-12 inches, carry up to several pounds and should only be used for the smallest spotters (Mini-MAKs and the like). Besides the low weight capacity, these tripods often can’t stably tilt back to look very high and have to be used on a flat surface, limiting their usefulness. Their advantage is extreme portability. A lightweight photo tripod can carry weights up to 10 lbs, can stand up to 65 inches high and usually has a ball or pan-type head allowing stable pointing in all directions. These are an excellent choice for the vast majority of spotting scopes, and are recommended for apertures up to 80mm. They are still light enough and can be collapsed to a reasonable size for convenient carrying. A medium or heavy-weight photo or video tripod can carry weights up to and beyond 25 lbs. Use these platforms for the heaviest, longest focal-length spotters, like the 80ED Refractor, Onyx, C90 and C130 MAKs and the C5. For astronomy or the most stable terrestrial viewing and photography, consider using a telescope mount that can be adapted to hold the 1/4x20 screw needed to attach a spotting scope.


	What kind of eyepieces can I use with my spotting scope? Most Celestron spotting scopes need no eyepiece beyond the zoom eyepiece that came installed as a part of the scope. This includes all the Ultima and Ultima ED series scopes, the C65 Mini-MAKs and the Mini-50 Zoom. The C50, C70, C90, C130, 80 ED Refractor, 102mm Wide View, Onyx 80EDF and C5 scopes can use the astronomical standard 1.25-inch eyepieces widely available in most parts of the world.


	What is a waterproof spotting scope? Waterproof scopes are designed to totally exclude water from the optical tube and also may be filled with dry, inert gas (nitrogen) as an additional barrier to internal moisture. There may be seals and optical windows too. The additional feature of rubber armoring is the final level of ruggedness and helps protect your scope from abrasion, damage or loss of collimation if you accidentally drop it.


	What is the resolution of my spotting scope? Resolution is a measurement of a spotting scope's ability to distinguish fine detail and produce a sharp image. Better resolution also delivers more intense color and often higher contrast. Resolution varies in relation to the size of the scope's objective lenses. Generally, a larger objective lens will deliver more detail to the eye than a smaller objective lens, regardless of the magnification. Actual resolution is determined by the quality of the optical components, the type and quality of the optical coatings, atmospheric conditions, collimation (proper optical alignment), and the visual acuity of the user.


	What does near focus mean for spotting scopes? Near focus is simply the distance between the scope and the nearest object you can focus on. In general, you can focus closer with lower magnification and smaller aperture spotting scopes.


	I want to use my spotting scope to take pictures – what’s its f-number? The f-number or focal ratio is just the focal length of the spotting scope divided by the aperture (diameter of the lens). It’s almost universally given as a quantity like f/5, f/2.8, etc., called the f-stop or photographic speed. These terms are used interchangeably. Example: an 80mm spotting scope with a 480mm focal length has a f-number of 6 and its photographic speed is f/6. Lower numbers mean the lens is delivering light more quickly and consequently shorter exposures can be used when taking a picture through the scope.


	What is the eye relief for spotting scopes? Eye relief is the distance (in millimeters) between your eye and the spotting scope eyepiece that allows the full field of view to be comfortably observed. It measures the spacing from the last surface of the eye lens of an eyepiece to the plane behind the eyepiece where all the light rays of the exit pupil come to a focus and the image is formed. Your eye should be positioned here to see the full field of view of the eyepiece. Eye relief should be at least 10mm, 15mm for the best comfort, maybe more if you wear eyeglasses. Put your eye so it's just behind the eyepiece to take advantage of its eye relief. You’ll lose field of view if you place your eye farther away and may even move your eye out of the beam of light from the eyepiece. Getting too close will prevent you from blinking and may also cause a black ring to appear around the field of view.


	What is the eye relief for spotting scopes? Eye relief is the distance (in millimeters) between your eye and the spotting scope eyepiece that allows the full field of view to be comfortably observed. It measures the spacing from the last surface of the eye lens of an eyepiece to the plane behind the eyepiece where all the light rays of the exit pupil come to a focus and the image is formed. Your eye should be positioned here to see the full field of view of the eyepiece. Eye relief should be at least 10mm, 15mm for the best comfort, maybe more if you wear eyeglasses. Put your eye so it's just behind the eyepiece to take advantage of its eye relief. You’ll lose field of view if you place your eye farther away and may even move your eye out of the beam of light from the eyepiece. Getting too close will prevent you from blinking and may also cause a black ring to appear around the field of view.

Will my spotting scope let me see bullet holes in targets on a shooting range?

Whether or not your spotter will be able to clearly see or resolve a bullet hole in a distant target depends on the size of the bullet, the size of hole it makes and the range to the target. These numbers are used to calculate the angular size of the bullet hole. Then you can compare the angular size to the resolving power of your scope to see if it’s adequate.

First, we’ll assume the bullet hole is the same size as the bullet. The holes are often larger, so this is a conservative assumption.

If necessary, convert hole size and range to inches.

To calculate the angular size of the bullet hole, divide the size of the bullet hole by the range. Multiply the result by 206,265. The number you get will be the angular size in arc-seconds of the hole as seen from the shooting line.

Compare this number to the following chart to find out which scope is best for your target spotting.

Scope diameter (mm)	cLEAR Resolution (ARC-SEC)
50	3.7
60	3.1
65	2.8
70	2.6
80	2.3
90	2.1
100	1.9
130	1.4

Example: a 50-caliber bullet hole in a target at 1000 yards. What size scope is the smallest I can use to spot this hole?

1000 yards equals 1000x3x12 or 36,000 inches. 0.50 divided by 36000 is 0.0000138.

0.0000138 x 206265 = 2.8 arc-seconds

A 65mm scope will clearly resolve 2.8 arc-seconds. So you would need at least a 65mm objective size spotting scope to see your shot.

Other factors affecting your ability to see the bullet hole are air quality, steadiness of the air and lighting conditions.