Not so long ago, finders were little straight-through refractor telescopes and your only choice was the size. Today we have many more choices, and while personal preference is a major factor in picking a finder, not all finders work equally well when faced with light pollution. When dealing with significant light pollution, I've found that a green laser finder combined with a traditional finder-scope works best.

Let me explain why and share my thoughts on how the various types of finders work under washed-out skies....

TELRAD Finders

TELRAD-type finders are very popular. They work by projecting a “reticle” out at infinity. So when you look through one, you see the sky (unmagnified) with an aiming pattern superimposed (think of a fighter-pilot’s look up display). The aiming pattern can be a single dot (so called “red-dot” finders), a pattern of concentric circles (say 4, 2, and ½ degrees in diameter), or something even fancier. In dark skies you can use these with a good set of charts (some charts are even tailored for use with TELRADs) to star-hop very efficiently to your target. Unfortunately, if there is significant light pollution you usually can’t see enough stars to star-hop with a TELRAD. Also, the glass lens of the TELRAD doesn’t make it any easier to see the stars, and even worse, local stray light often glints on the TELRAD lens.

For these reasons, I have found that TELRADs are not useful in light polluted environments: you can’t see enough to star-hop with them. Under washed-out skies they are only good for aiming your scope at relatively bright stars. This can still be useful as the first step, allowing you to then use a more “traditional” finder-scope to star-hop from that star to your target.

Laser Finders

Take a green laser, attach it to a telescope, and you have a laser finder. People tend to either love them or hate them, but in my experience they work very well in light polluted skies. Perhaps I’ve been lucky, but even the cheapo green laser I’ve purchased shows up pretty clearly against light polluted skies. In fact, even with a full moon the beam is clearly visible if you simply sight along the laser. I find laser finders much better than a TELRAD or red-dot because you can simply look up at the sky, find that hard to see 4.5 magnitude star (remember, the sky is washed-out), and then you can swing the telescope to point right at it, without ever looking away from the star. For me that works much better than trying to sight that faint star through a TELRAD.

The problem with laser finders is that they don’t work well when it gets cold. Lithium batteries help, but somewhere between 40F and 30F my cheapo green laser pointers fade out. A premium green laser pointer might do better, but even those fade out at some point. Green lasers have two other drawbacks. First, you need to be alert and not accidentally point one towards an aircraft (remember to turn it off once you’ve pointed your telescope). Second, green lasers are banned at many star parties. So as much as I prefer my green laser finder, I also have a simple red-dot finder to use on cold nights or at star parties.

Finder-scopes

Many amateurs (and telescope makers) don’t bother with finder-scopes anymore, using TELRADs to do their star-hopping. But as I mentioned above, TELRADs aren’t very useful in washed-out skies. If there is moderate to significant light pollution, a traditional finder-scope is essential. It’s the only way you can see enough stars to find your way around; in some cases, it’s the only way you reliably see stars fainter than 4th magnitude.

Finder-scopes are available in a variety of sizes. A 6x30 finder-scope is the minimum useful size. I find an 8x50 finder-scope ideal for use in light polluted skies. Finder-scopes are available in straight-through, right-angle, and right-angle, correct image (RACI) versions. Depending on your telescope, a right-angle finder-scope can be more comfortable (e.g., on a Newtonian reflector). I find RACI finder-scopes very convenient because you don’t have to mentally translate between a star atlas and the finder-scope view. But for many years I used a straight-through finder-scope and I never had trouble making the translation. So it really is a matter of what you prefer.

Ultra Wide-Angle Eyepieces

While technically not a finder-scope, modern ultra wide-angle eyepieces combined with relatively fast (short focal ratio) scopes produce views that are often 2 or even 3 degrees across. It is quite possible to use such a combination as an effective finder-scope. All you need to do is pick a suitably bright star as a “jump off” point, point your telescope at it (perhaps using a red-dot or laser finder), and then star-hop using your main telescope. I personally find that my main telescope shows too many stars, making it hard to match the views to a star chart. But it is definitely workable.

Summary

For use in washed-out skies, I find that a green laser finder combined with a RACI finder-scope works best for me. Even with significant light pollution, the green laser lets me quickly point my telescope to the faintest stars I can see, and the RACI finder-scope shows me enough stars to let me star-hop from there. If the night is too cold for the laser finder or if I’m at a star party, I use a simple red-dot finder in place of the laser finder.