Quote:
Originally Posted by ianB
I dont know what the compression ring is but I expect it just replaces a screw and you just tighten the diagonal.
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As you'll see in the diagonal you have now, the ends of screws area used to secure the eyepiece in the diagonal, where the ends of the screws don't have much surface area and they mark the eyepiece barrel when they dig in.
With a compression ring, there is a (usually brass) ring in that end of the diagonal and you put the eyepiece in there as usual and as you turn the screw, it grips the eyepiece barrel all the way around, so it's more secure and makes less/no mark around the eyepiece barrel.
