How Do I Usually Align Finderscopes?

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Written By: Ed Anderson
Category: Learn

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.

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

Deciding On The Alignment Target

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 difficult to get the alignment correct.

Set up your telescope so it is level. Pick out a distant target, at least 100 yards away, and preferably ½ a mile, 1 KM, or farther. The farther, the better. This is your alignment target.

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. Anything that will provide a precise, distant point to target.

Steps for Aligning The Finder With Telescope

Here are the steps to follow.

  1. Remove the lens caps and put your lowest-power eyepiece (the eyepiece with the highest number) in the diagonal or focuser. Now look along the tube of the telescope, not the finder, and point the optical tube in the direction of the target. Now look through your eyepiece and adjust the optical tube until you can see that pole, chimney, or whatever target you’ve chosen. Get your target centered in the field of view of the eyepiece. Remember, you haven’t used the finder scope at all until this point.
  2. 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.
  3. Switch to a high-magnification eyepiece (the one with the lowest number) and again, get that target centered as best you can.
  4. 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.
  5. Lock the scope into position in any way you can. You don’t want the telescope to move.
  6. Look through the finder and spot the target.
  7. Red dot at full intensity when viewed through a red dot finder
    The 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. Depending on your finder type, in place of the red dot, you might find a circle or a crosshair.
  8. Using the adjustments on the finder bracket, adjust the finder until the target is centered in the finderscope. Typically, there are screws on the side, top, or bottom that allow you to adjust the position of the finder.
  9. 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.
    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.
    Gskyer telescope's straight through magnifying finderscope
    The two black adjustment screws on a magnifying 6×30 finder scope
  10. Go back to the eyepiece and make sure the scope has not moved. The target should still be centered.
  11. 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.

The Final Confirmation Before Observation

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. My first step during each observing session is to pick a bright star and use the finder to point the optical tube. 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 only takes a few seconds, and will save a lot of effort throughout the evening, as your finder and your scope will be in the best alignment possible for the evening.

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