Why worry about a finder scope? Most scopes sold today are go-to jobs. Beyond sighting alignment stars, a good finder can come in handy for go-to users on those not-unheard-of occasions when the scope computer misses a target. They can also be useful for finding objects the old-fashioned way—by star hopping, perhaps to objects not in the hand control's database. Although all go-to telescopes come with finders of some sort, these may not be adequate for much beyond sighting alignment stars. When it comes to a better finder for a scope, there are essentially two choices: zero power and optical.
Many lower-priced go-to telescopes come equipped with zero-power finders, most often of the red-dot variety. This type finder works okay, but it can be difficult to accurately place a small dot in just the correct position among the stars. A better zero-power unit is the Telrad ($40). The late American amateur astronomer
Steve Kufeld came up with what was the first commercially marketed zero-power finder, the Telescope Reticle Aiming Device—Telrad. Through clever use of a red LED-illuminated reticle and a beam-splitter window, the Telrad seems to project a bull's-eye onto the night sky. The three concentric circles that form this bull's-eye represent angular distances in the sky of 4°, 2°, and 0.5°. These circles, seeming to float among the stars, make aiming a telescope simple and intuitive. There are no upside-down images to figure out as in a finder scope. The reticle circles make it easy to position the telescope accurately when searching for dim deep sky objects. The Telrad mounts on a rectangular plastic base that is affixed to a telescope's tube by included double-sided tape.
The Telrad is not the perfect solution for star hopping, however. It does not collect more light than the unaided human eye and thus will not show stars dimmer than those that can be seen with the naked eye. That may make it difficult to find objects in star-poor areas. A good-size optical finder, one with an aperture of at least 50 mm, is a nice addition to a telescope equipped with a zero-power finder or replacement for one of the too small 30-mm finder scopes that come with less-expensive telescopes. A 50-mm will show stars down to at least magnitude 8, which includes every star plotted on Sky Atlas 2000. Good finders are not expensive, either, with decent Chinese-built models going for $75 or less.
Optical finder scopes are fine, but many amateurs do not like the way a normal finder telescope inverts its image or the way optical finders make a person contort his or her body to look through them when the scope is pointed near the zenith. Orion U.S. has a solution. Its 9 X 50 mm RACI (right angle correct image) finder yields an upright image of the sky with a comfortable built-in star diagonal that delivers images correct right to left so what is visible in its eyepiece exactly matches what is on charts. This is accomplished by an "Amici"-style prism contained in the finder's built-in star diagonal. The RACI works well, and at $80, it is not much more expensive than a normal "straight-through" finder scope.
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