Last updated: 27 May 2004

Subject:	Very easy Hartmann mask for ETX-105
Sent:	Wednesday, May 26, 2004 15:10:04
From:	Leo Bodnar (lbodnar@dsl.pipex.com)
I found quite a good source for Hartmann masks for ETX-105. They are
covers for those CD-R sold on spindles in 10, 25, 50 quantities without
jewel cases. I had a few and some of them fit tightly some a bit loose -
choose to your taste.

1. Cut the holes with exacto knife. Plastic is a bit brittle so work
your way slowly from both sides.

2. Spray some paint on the outside to make sure that even if it ever
flakes off it's going to be on the outside from the front lens. Or use
sticky tape. Should not necessarily be 100% optical black!

3. I have cut off three of those little tabs that lock the cover when
twisting it on the base. Don't! Leave one on and use it as a flag to
indicate "up" position for the Mask - works even in darkness! That way
you are going to be consistent with image orientation with relation to
focussing in/out.

4. Keep another CD-R "cake" cover as a quick scope front element
protector. Much lighter, cheaper and easier to find when dropped in the
field. Use original one when transporting. Plastic one fits on top of
metal one when not needed.

Best wishes
Leo Bodnar
Hartmann Mask

Mike here: For more on the usefulness of the Hartmann Mask see the article '"Hartmann Mask" Focusing Aid'.

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