Solar Finders: Safely Target the Sun with Your Telescope

Last month I wrote about making your own solar filter. Now you’re all set to look at the Sun, right? So how do you aim your scope at it?

Come on, how hard can it be? It’s right there, big and bright and half a degree acro. . . ss. Oh, yeah. It only covers half a degree of sky. And it’s too bright to look at with your Telrad or optical finder. (Seriously, don’t do that.) The Sun is too bright to even sight down the your telescope’s tube at safely. With the filter on your scope, you won’t see any glow through the eyepiece until you’re right on it. Until you’ve tried it, you’d be amazed at how difficult it is to aim a telescope at the Sun without some kind of finder.

Here’s how to make one.

There are two basic ways, and both use the Sun as part of the system. You can either cast a shadow onto a target or cast a beam of light on a target.

The simplest finder I’ve seen consists of two tabs of masking tape. Stick one on the front edge of your scope with an inch-long tab standing out. Put another tab a foot or two back, in line with the one on the front. Poke a hole in the middle of the front tab, and move the scope around until the ray of light shining through the front tab hits the back tab. Center it up, and you’re on target.

Cut the front tab into an arrow shape with its point half as high as the rear tab and you get the same effect with a shadow instead of a bright spot.

Masking tape isn’t very elegant, and it’s hard to get the two tabs precisely aligned. You’re better off building a finder that you can mount solidly on your scope so it’ll remain aligned from use to use. Designing it to fit on your regular finder’s mount is a good strategy, since you won’t be using that finder by day anyway.

A 4- or 5-inch length of 1-inch-diameter PVC pipe makes a good finder body. Cap the front end and drill a small (1/16-to-1/8-inch) hole in the middle of the cap, then stretch a section of white plastic bag across the back. When aimed at the Sun, a bright spot of light shines on the white plastic. After you’ve found the Sun in the scope for the first time with the finder attached, put a black dot in the center of the bright spot with a felt marker and you’ll have no trouble finding the Sun again.

One nice variant is to open the body of the finder so you can look at the bright spot on the screen from above. That eliminates bending down to see it. I made the finder below from two pieces of flat PVC plastic and a piece of clear Plexiglas, which I frosted with fine sandpaper to make a screen. The upright sections are hinged so they fold down out of the way when not in use.

David Lazaroff has made a clever design using the plastic spout from a detergent jug. The front end has a nifty cross-hair design molded in, so all David had to do was remove the opaque back and glue a translucent plastic cap from a spray bottle on it. He then sanded the screw thread section of the spout to fit the curve of his telescope, threaded a piece of nylon cord through holes in the spout, and added a cord lock to hold the whole works in place. When aimed at the Sun, it projects a beautiful cross hair on the end cap.

You can undoubtedly come up with several designs of your own. Just about anything that casts a shadow or a bright spot on a screen will do, as long as you’re not magnifying the Sun’s intensity through a lens.

Happy hunting — and finding!

This article originally appeared in print in Sky & Telescope's July 2017 issue.

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