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Old 14-02-2008, 02:02 PM
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Starkler (Geoff)
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Join Date: Sep 2004
Location: Melbourne
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What is probably confusing you Eric is actually identifying what you seeing. ie what reflection belongs to what.

What can you help here is if you get a piece of paper and fix it to block the view of the primary, so that you only see the secondary in the cheshire. Likewise when trying to align the secondary under the focuser, slipping a piece of white paper against the opposite tube wall will help.

As for out of focus cross-hairs, it shouldn't be too much of an issue given that centering them on the mirror centre spot isn't all that critical. Somewhere inside the inner part of the ring will do. It also helps to bring your eye back away from the cheshire to view both cross-hairs and primary centre ring.

If you are using laser secondary mirror pointing IS critical.

A long cheshire like the Orion is better for two reasons. Firstly the greater length between the peep hole and the cross hairs allows much better accuracy due to reduced parallax error. Secondly it is long enough that the inside edge of the tube can be used as a guide for aligning the secondary under the focuser. You rack your focuser in or out until the secondary edge appears just inside the end of the cheshire tube.
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