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Old 22-09-2017, 08:36 PM
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Wavytone is offline
Join Date: Jul 2008
Location: Killara, Sydney
Posts: 4,147
This depends on the focusser or star diagonal it fits into, as well as the eyepiece barrel. It also depends on the user - the screw only needs to be tight enough to stop the eyepiece falling out - not moor a cruise liner.

The very cheap ones have a simple retaining screw which as you suggest will lightly scuff the barrel of most eyepieces.

One simple solution is to find a nylon screw that fits instead of the steel one - this won’t mark eyepiece barrels. Nylon screws are often used in electronics and are available in small sizes

The better draw tubes or diagonals have a “compression ring” fitted inside - this is a captive ring that squeezes around the perimeter of the eyepiece to hold it. Slight scruffing might be evident after a lot of use but it’s much better than a simple screw. In this arrangement it’s not uncommon to find as many as 3 screws used to tighten the compression ring on focussers intended to take heavy loads like DSLR bodies, filter wheels or big eyepieces - these loads can be several kilos.

If the eyepiece barrel is stainless steel or steel hard-chrome plated, this will withstand abuse much better than plain anodised aluminium barrels. But that is something you’ll find on premium eyepieces, not budget ones.

Lastly 30 years ago a different solution was quite common which in some respects was better - no screw at all - the eyepiece barrel was a very thin tube with a split cut down the side - and the eyepiece was a firm fit and simply pushed in. This was perfect for small lightweight eyepieces of that era, but inadequate to hold the monster 2” handgrenades from Televue and ES which can weigh a kilogram, nor could you trust it to hold a heavy camera.

Last edited by Wavytone; 22-09-2017 at 09:03 PM.
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