How Does a Spotting Scope Work?
Refracting Telescopes
Spotting scopes are essentially compact amateur astronomy telescopes that have been optimized for use during the day, portability, and looking at ground objects. Because of these considerations, they are usually refracting telescopes. Refractors use lenses to concentrate light and achieve magnification, and spotting scopes are based on the venerable Galilean model. This uses a convex objective lens, and the bigger the objective lens, the greater the basic magnification power. The Keplerian model is not used for spotting scopes because it turns the image upside down.
Periscope Viewing
The viewing mount and eyepiece of a spotting scope are done either using the simple, straight-through telescopic model, or the periscope model. In the latter, the viewing mount is on the side of the bottom end of the spotting scope tube, usually pointed up for ease of viewing. Light collected and concentrated by the objective lens is bounced off a mirror or prism along an angle to the eyepiece, just as in a periscope.
The Eyepiece
The main accessory for spotting scopes is the eyepiece. While sometimes fixed and singular, many spotting scopes have an eyepiece with a zoom lens function. Others allow eyepieces to be removed and swapped for eyepieces with differing optical features. Regardless of the actual working set-up, changes in magnification are always controlled at the eyepiece, and not the objective lens.
Camera Adapters
Many spotting scopes that feature removable eyepieces are also capable of fitting adapters for cameras. The specific adapter depends on the features of the camera in question, but the general principle is to replace the eyepiece assembly itself with the lenses of the camera.
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