Finders

Do computerized telescopes need finders? Yes, of course - for finding and centering the initial two stars, if nothing else.

Like binoculars, finders are rated by magnification and aperture. Thus, a 5 x 24 finder magnifies 5x and has an aperture of 24 mm. Larger finders, such as 8 x 50 or 10 x 60, provide interesting views of star clusters in their own right and are precise enough to center objects for CCD imaging.

Should the finder have a diagonal? Maybe. An "elbow" or right-angle finder is much easier to use when sighting Polaris during polar alignment (Figure 4.7, p. 46). Particularly on smaller telescopes, access to a straight-through finder in that situation is blocked by the base of the telescope.

But a straight-through finder (Figure 6.11) is much easier to use the rest of the time. My technique is to keep both eyes open, one of them looking through the finder and the other viewing the star directly, then move the telescope to make the two images coincide.

With a computerized telescope, you do not need to see faint stars through the finder. Accordingly, nonmagnifying LED finders (Figure 6.12) are popular and convenient. Using a beamsplitter, an LED finder displays a red dot that seems to be superimposed on the sky. You simply sight along it, looking directly at the sky, and put the spot on the star that you want to view. A more elaborate type, the Telrad (invented by Steve Kufeld and available through many telescope dealers), projects a pattern of circles.

Sometimes you need both kinds of finders on the same telescope. An ETX-90, for instance, is much easier to polar-align if you have both a straight-through

Figure 6.11. Straight-through 8 x 50 finder on a Meade LX200.
Figure 6.12. Nonmagnifying LED finder on Celestron NexStar 5. Seen through its window, a red spot appears superimposed on the sky.

LED finder for rough alignment and a right-angle magnifying finder for precise pointing. Fortunately, LED finders are easy to add; they attach with adhesive pads, requiring no modification to the telescope.

Was this article helpful?

0 0

Post a comment