As the name suggests Finderscope is a small telescope mounted on the main astronomical telescope that is used for finding the celestial objects. Finderscope has low magnification as compared to the main telescope which allows user to easily spot and aim the telescope at desired astronomical objects.
Why is it important to Align a Finderscope?
Before understanding why it is important to align the finderscope? First, let’s discuss how finderscope works.
When we look through the telescope eyepiece we see a small part of the sky because of its higher magnification. The area is so small that it gets very difficult (not impossible) for a user to locate anything through the telescope eyepiece.
This is why finderscope comes in handy here. Because of their lower magnification, it covers a wider area of sky. Which makes it easier to aim at the object you are after.
Now to answer the question why is it necessary to align it first? Because once the finderscope is perfectly aligned, whatever we aim with the finderscope will be visible in the main scope.
There is two common type of finderscope popular in the market, Optical finders and Reflex finders.
Optical finders is essentially a small low power wide angle telescope with a set of the crosshair. The image is inverted in Optical finders (not a big problem once you get used to it) whereas Reflex finderscope projects a small red led dot on a small piece of glass to help center an object. It has zero magnification.
Both of them works on the same principle and it’s up to you to decide what you prefer. Now that we know what is finderscope and why is it important to align the finderscope, let’s learn how to align both of them properly.
How to Easily Align an Optical Finderscope.
Aligning a finderscope is so easy that even a beginner user can do it in less than five minutes. Before starting the process, pick a stationary object at least quarter a mile away such as telephone poles, treetops, mountain peaks or anything. One thing I forget to mention, run the alignment process during the day since objects will be clearer to see.
Picked a stationary object? Let’s start,
Put a low power eyepiece (one with highest focal length) into the focuser. Now point the telescope in direction of the object you choose earlier for alignment. Move the telescope until the target is centered in the eyepiece.
Next, look through the finderscope where it is pointed. You will notice that image is upside-down. Don’t worry it is perfectly normal.
Now, there will be two alignment screw and one pivot screw located on the finderscope bracket. Turn them one by one until the object is centered in the crosshairs of the finderscope.
Once the object is centered in finderscope, again look through your telescope eyepiece. If the object is at center then your finderscope is perfectly aligned with your telescope. If not, repeat step 1, 2, 3 with another stationary object with different eyepiece (20mm or 25mm would be a good choice.)
How to Align a Reflex/Red-dot Finderscope.
Aligning the telescope with red-dot finderscope is even easier since the image is correct.
Do the same thing you did in step 1 of aligning with optical finderscope. Use the low power eyepiece and move the telescope until the object is centered in the eyepiece.
Next, turn on the finderscope. You will see a red led dot on a small piece of glass. Now, turn the altitude-azimuth control knob until the object is centered on the red dot.
Check again through your eyepiece to make sure your object is still at the center. If it is there, congratulation you have properly aligned your red- dot finderscope with your telescope.
Here a a video tutorial to help you more on that:-
Some more useful link:-
Collimation is a process where we align the primary and secondary mirror. It is another important process which should be done before taking your telescope out for stargazing. This article will help you to understand what is Collimation and how it is done.
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