Quote:
Originally Posted by Merlin66
Barry,
I agree with your terminology, but surely the outcome is the same?
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For most intents and purposes of tracking, as long as your RA axis is aligned with the earth's axis you won't generally notice and problems with orthogonality. It is when you want to drive the assembly with a set of coordinates to a precise position that orthogonality is actually noticed.
With a good GEM the orthogonality is usually extremely close and can be ignored however the errors in gotos can usually be traced to cone error which is the alignment if the OTA to the declnation plane, assuming you are already correctly polar aligned. This can be corrected by shims if vertical alignment is required.
I have not had much experience with GEM's (My son has my G11 and I have never used it myself). However I have had a lot of experience with fork mounted LX200's and developed methods of measuring as well as correction. The first step is to get the Dec axis orthogonal to the RA axis and when this is correct (In could never get better than about 3 arc minutes) then get the OTA orthogonal to the dec axis to remove the cone error. These corrections I did for many people to get their gotos reasonable (about three arc minutes anywhere).
Barry