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Hi John..my apologies...I should have mentioned that you place the paper ribbon around the circumference of the optical tube alongside the focuser...and there you can measure the base of the focuser as to ascertain the middle of where the EP holder..Looking at the focser on my Saxon Dob I'll label the sides top, bottom, left, right...I measured the bottom to find the middle of the EP holder..then measure the right side to find the middle of the EP holder..as the paper ribbon is against the right side..mark the middle of the EP holder on the paper ribbon..and then mark the optical tube so you can replace the ribbon to EXACTLY the same spot...when you remove the ribbon then fold it in half..you should have a creasemark on the mark from the middle of the EP holder of the focuser..and another creasemark which will be the exact opposite of the optical tube when you replace the ribbon...all you need to do is mark the spot that you had measured from the bottom of the focuser to find the middle of the EP holder by using a straight edge along the creasemark on the ribbon on the opposite side of the focuser..this should mark the spot of the middle of the EP holder of the focuser on the exact opposite side of the optical tube!!
Another way to find the middle of the EP holder is by using a carpenters square, a cheshire collimator and a ruler.
Place the collimator into the EP holder...place the square's handle in line with the tube with the number side against the right side edge of the focuser pointing away from the tube..all you need to do is measure from the centre of the collimator to the number edge of the square..
Once again..sorry for any confusion.
Cheers!
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