Choosing Your Spotting Scope
A spotting scope is a compact telescope that is usually designed for terrestrial viewing and when you require a magnification beyond the range of a typical pair of binoculars. When deciding what type of spotting scope to buy for bird watching there are a number of optical and design features that you should keep in mind.
The magnification power of a spotting scope is usually between between 15x and 250x. Ideally, the objective lens should be at least 60 mm in diameter to provide a bright image.
To change magnification, spotting scopes will come with a number of fixed-length eyepieces or a single zoom eyepiece. When using a spotting scope for birding begin with a low power magnification in the 20x to 30x range. Once you have spotted your target you can then switch to a higher magnification. A good eyepiece will have a bayonet fixing for a quick change and a simple focusing mechanism.
Zoom lenses can alter the magnification power from 20x to about 60x with a single adjustment. As with binocular zoom lenses, scopes will suffer from less light and a narrower field of vision as the magnification increases so the best policy is if you can’t afford interchangeable eyepieces buy the the highest zoom lens spotting scope you can afford.
The best spotting scope lenses are made from fluorite-coated, HD (high density), or ED (extra-low dispersion) glass. The difference in brightness and image clarity between high-quality scopes those made using standard glass is particularly noticeable in low-light viewing conditions and at high magnification power.
The larger the objective lens at the end the end of the scope, the brighter the images because a large lens gathers more light. However, it also makes the scope heavier which is why weight is usually included in any specifications and you should consider this before buying a scope particularly if you plan on carrying it for any length of time.
There are two methods of focusing a spotting scope. A grip around the scope barrel can be turned for rapid focusing or there will be a knob which is turned which although slower, can be more accurate.
The distance between the eye lens and the point where the pupil is positioned for full field of view varies from eyepiece to eyepiece. Check that it is within the right length particularly if you wear spectacles so you can obtain the full field of view.
Serious bird watchers will always use a tripod as in outdoor conditions the images will be much better. As well a being more stable a scope supported on a tripod is ready for use the moment your target appears. Choose a mid-weight tripod with legs that are simple to adjust and a flip-lock design for a secure mount.