Spotting scopes (also called fieldscopes) are general-purpose telescopes, used for:
- Photography (a standard scope is usually equivalent to a 500mm f8 or f11 camera lens).
- Bird-watching and wildlife observation.
- Astronomy (though dedicated astronomy telescopes are better for astronomy).
- Target or range shooting (including archery, air rifle).
Spotting scopes are more powerful than standard binoculars. They are used when more magnification is required and when a tripod can be used. It is not practical to use one hand-held like binoculars.
Standard binoculars are 7×50, 7 times magnification with a 50mm diameter objective (front) lens. Smaller 7×35 binoculars are also popular. Larger and higher magnification binoculars are available but like spotting scopes, a tripod is required unless the binoculars are stabilized .
Most spotting scopes are refracting telescopes (uses lenses), not reflecting telescopes (uses mirrors).
Spotting scopes start at 20×50 (20x magnification with a 50mm objective) and can reach 100×100. 20x to 60x zoom spotting scopes with a 60mm objective (20-60×60) are a common configuration.
Popular brands include Bushnell (Elite, Spacemaster), Celestron, Nikon (ProStaff), Barska, Leupold (Wind River), Kowa, Pentax, Swarovski, Alpen, Burris, Leica, Zeiss, Meade, Tasco, Konus, NcStar, Simmons, Winchester, Brunton, Opticron, Swift, BSA, Fujinon, Skyline, Eagle Optics, Redfield, Weaver and Bausch & Lomb.
Prices can be less than $100 for budget brands, to a few thousand dollars for premium brands.
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Spotting Scope Zooms, Magnification and Lens Size
Quality optics and a large objective lens are more important than magnification.
The bigger the objective lens, the more light the telescope can collect. At higher magnifications, the image becomes darker. A large lens is therefore important. Light-gathering-power is proportional to the area of the lens or the square of the diameter:
- A 60mm lens is 50 percent brighter than a 50mm lens.
- An 80mm lens is 80 percent brighter than a 60mm lens.
- Spotting scopes top out at about 100mm (4 times brighter than 50mm).
The image also becomes blur at higher magnifications, especially for lower quality scopes, and field of view is reduced. A high maximum magnification specification may therefore look good on paper but can be unimportant.
Zooms add complexity, increasing cost and lowering optical quality (though not in premium brands). For good optical quality and the most bang for the buck, a non-zoom telescope can be a good choice.
The focus should not change when the scope is zoomed, though this might be tolerable in a budget scope.
Angled Spotting Scopes
In a straight scope the eyepiece is directly behind the objective lens, in a straight line, or offset to the top but still in a parallel line.
Angled 45 degree spotting scopes are popular. The eyepiece tilts up 45 degrees. They allow the user to look down when looking through the eyepiece. The telescope can be mounted lower and is especially useful for shooters who shoot lying down.
They also allow the telescope to be used for astronomy, pointing high up at the sky, without having to lie flat on the ground to look through the eyepiece.
Spotting Scope Features
Useful features include:
- Wide field of view. Field of view decreases with increased magnification, but for the same magnification some (more expensive) scopes can show a wider field of view.
- Waterproofing. Spotting scopes are used outdoors, in rain and fog.
- 1/4 and 3/8 inch screw sockets for standard camera tripods.
- Rubber outer layer for shock protection.
- Optional T-mount adapter for attaching SLR cameras.
- Objective lens filter thread. For fitting a clear protection filter (like for camera lenses).
- Low minimum-focus distance. Depending on what the scope is used for, it may need to be focused as close as 20 or 30 feet.
- High eye relief. This is the distance between the eyepiece and the eye. High eye relief (15 to 20 mm) is useful for wearers of glasses (spectacles). Eye relief reduces as the scope is zoomed (the eye needs to be pressed closer to the eyepiece), another reason why high magnification isn’t always good.
- Fog-proof nitrogen-filled lenses. This stops the lenses from misting up when the temperature changes.
- Low weight. The scope might need to be carried through miles of countryside.
- Removable eyepiece. This allows high and low power eyepieces to be used instead of a zoom. Some scopes use custom eyepieces but others can accept standard 1 1/4 inch telescope eyepieces.
The Best Spotting Scope
Anyone unsure of which type of spotting scope to get can start with a budget 20-40×60 or 20-60×60. Try-before-buy is important as the optical quality of budget scopes can vary greatly.
Only with some experience with the scope will it be possible to determine if an upgrade is required: in optical quality (resolving power, contrast etc), field of view, objective size, magnification or other features.
Many applications are not demanding and a budget scope will do just fine. Even if a better scope is purchased later, the budget scope can be used in rough situations (on a boat, in bad weather, in muddy areas, with children) where an expensive scope can’t be risked.