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Saturday, 11 December 2010

How to align the finder scope with the main scope?

The finder scope only works to its purchase when it has been aligned with the main scope, so the two are aiming at exactly the same spot. This is easy to do.

It is more convenient to align the finder scope while it's still light outside. A good time to do it is after the telescope has been set up but before the Sunset.

First, put a low-power eyepiece (with long focal length) in the eyepiece holder (focuser) of the main telescope. Looking into the eyepiece, centre a distant object in the field of view — the top of a telephone pole, a treetop, or a chimney on a house. The object should be at least a quarter-mile away. Now look through the finder scope and see if the object appears in the centre of the finder's field of view (where the crosshairs intersect). If it does not, use the adjustment screws on the finder scope bracket to adjust the aim of the finder until the object is centred. Then, look back into the telescope eyepiece and make sure the object is still centred there as well. If so, you're done. If it is not, repeat the procedure, being careful not to move the main telescope while you're adjusting the finder scope positioning.

When the distant object is centred in both the main telescope and the finder scope, the finder scope has been properly aligned and ready to use. Verifying the finder's alignment should be one of the steps you go through each time you set up for an observing session.

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