Red dot finderscope fixed to Meade Infinity 70 — A red-dot finderscope attached to a scope’s optical tube

Regardless of what kind of finder you are using, after a finder is mounted on the optical tube of the telescope, you will need to fine-tune where it is pointing so that it aligns perfectly with the field of view of the telescope. This procedure is fairly simple.

The key thing is that you are aligning the finder with the telescope, not the other way around.

You want to do this during the day using a fixed land object. At night, the things in the sky are moving, which makes it more difficult to get the alignment correct.

During the day, set your telescope so that you can see a distant object; at least ¼ mile away and farther is better. I prefer the cross arms on a telephone or power pole. That gives me a very well-defined target right where the cross arm meets the pole. But the top of a chimney, a letter on a distant sign, or something similar can work as well. This is your alignment target.

The mounting bracket of the finder usually has adjustment knobs or screws to move the finder about so you can get the finder and the telescope perfectly aligned. If the holder does not keep the finder firmly in place, it will frustrate your efforts to use it.

Here are the steps to follow.

Using your low-power eyepiece, point the telescope at the target and get it centered in the field of view of the eyepiece. Ignore the finder for now.

Viewing a telephone post through an eyepiece — Viewing and centering a telephone post through a low-power eyepiece (image taken using an iPhone). The view is inverted since the telescope I used is a reflector, which gives inverted views.

Switch to a high-power eyepiece and again, get that target centered.

Close up view of the post through a high power eyepiece — Smartphone image of the view of a centered telephone post through a high-power eyepiece.

Lock the scope into position in any way you can. You don’t want it to move.
Look through the finder and spot the target.

Red dot at full intensity when viewed through a red dot finder — The visible red dot is slightly off the target (the telephone post) that we locked earlier on the eyepieces. I’m using a simple red dot finder from Celestron for this demonstration.

Using the adjustments on the finder bracket, adjust the finder until the target is centered in the finderscope.

Adjustment knobs for moving finderscope red dot — Red dot’s position adjustment knobs are on both ends, and there is a knob to turn the red dot on/off or to increase its brightness in the middle.

Red dot centered on the telescope post — By using the position adjustment knobs, the red dot now coincides with the portion that we earlier centered on the eyepieces, i.e., the cross on the top of the telephone post.

Go back to the eyepiece and make sure the scope has not moved. The target should still be centered.
Check the finder again and make any final adjustments.

When the finder and the telescope are both lined up at the same point on your target, you are all set and ready to take your telescope out under the stars.

Finders have a tendency to get bumped or moved, especially if you take off at the end of your observing session when you put the telescope away. When you first start an observing session, do a check using a bright star. You should be able to do this quickly, so the fact that the star is moving should not be a problem.

Put the star in the center of the finder
Look through the eyepiece and center the star in the eyepiece
Go back to the finder and make any small adjustments that may be needed to center the star
Compare the view in the eyepiece and the finder to be sure they agree

This quick tune-up at the start of your observing session will save a lot of time throughout the evening, as your finder and your scope will be in the best alignment possible for the evening.

How Do I Usually Align Finderscopes?

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