Re: east/west Plate solving with an SCT

Howard Hedlund

Remember that we have a very quick and easy method for measuring orthogonality - the first step in correcting it.   
Go to page 52.   These instructions, of course, are for the keypad, but the concept applies easily to computers and plate solves as well.  By doing a little high-school trigonometry (remember to cut the measured error in half), you can get a precise measurement for shim thickness.  Trial and error is trivial on a 130, and usually unnecessary anyway.  On a big Cassegrain, trial and error is a major pain in the butt, so getting it real close to begin with is a good plan.  Understand as well that the error you measure will probably include some portion from shift/flop/movement.  Still, I think that fixing the orthogonality with this method will help, and it will mechanically reduce one important error source.  HH

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