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Dovetail rail not parallel to RA Axis?

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#1 Charles Hall

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Posted 20 February 2013 - 10:28 AM

I finally got around to trying check all the alignments on my LXD75. It turns out I had to adjust the end of my OTA up 1/8" above parallel to it's dovetail rail for the RA Axis to align.

This is an old Celestron C8 taken off a fork mount and with a 3rd party dovetail rail attached. I started with the rail parallel to the top of the telescope, but to make it align on the mount I ultimately had to adjust the front end up 1/8".

This strikes me as strange. It would appear to mean that either: a) The outer shell of the C8 is not parallel to it's internal optics, or b) the slot where the dovetail attaches to the LXD75 is not parallel with it's own RA axis.

Is this normal? Or do I have something else going on that I do not understand?

Thanks,

Charles Hall
Raleigh, NC

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#2 jrcrilly

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Posted 20 February 2013 - 10:36 AM

a) The outer shell of the C8 is not parallel to it's internal optics,


That's pretty much a given with an SCT due to its secondary-only collimation adjustment. The good news is that Meade's three star alignment takes that into account so no mechanical correction is required.

#3 Cliff Hipsher

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Posted 20 February 2013 - 01:42 PM

Yes, that is normal. In fact, if you look at pages 53 thru 55 in the LXD75 manual you will find 2 procedures used to make this adjustment.

What these adjustments take care of is Cone Error between the RA axis and the telescope optical axis.






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