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.
https://astro-physics.info/tech_support/mounts/keypad/keypad-manual.pdf   
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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