Chris Heapy writes:

>I believe I have a workable system using my guidescope setup, but I do not
>have any long exposures to prove it. The only variable that I don't have
>complete control over is the primary mirror moving within it's cell, though
>I suspect that different examples of the LX200, particularly the larger 10"
>and 12" models, exhibit considerable variation in the movement of the main
>mirror. I do know that I have virtually zero image-shift when focussing at
>high powers, but this is a separate (though related) issue, I think, from
>the mirror 'flop' due to an insecure mirror. I do think that if your own
>scope exhibits significant image-shift when focussing then there is a
>mechanical problem with your scope that needs to be rectified before
>attempting prolonged exposures using a guidescope

This is encouraging for me as I have a set of Chris's guidescope rings
(though no long exposures yet).

However I can think of another reason for trailing. Some users have
reported loose corrector plates. This would probably move even more easily
than the primary mirror, and might easily have been overlooked. A moving
corrector plate would introduce a large trail for even a tiny movement, as
the alignment of the secondary would be affected. Also it would be very
easy to correct, and so should perhaps be looked for first. A loose
secondary within a static corrector would also cause problems.

Nigel Puttick

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