Chuck wrote:
Very busy until the week of Aug. 26th. I'll have some breathing room then.
Thanks for the offer. I was able to make the repair affixing the mirror in a set position and miniminzed the perpendicular error to 0 arcmins at RA0h, 0 arcmins at RA18h, and 1.5 arcmins at the RA6h position. I tested the accuracy pointing with the Orion 10" Newt on the Synta mount EQ6 mount at last night's star party. After 3 star alignment and setting 4 pointing accuracy ehancement stars ("on the fly" synch of the star positions), the mount would do 50+ deg slews (Deneb to M11) with 0-10 arcmin pointing accuracy in the east hemisphere of the local horizon. This was sufficient pointing accuracy to quickly run through about 10 objects during the star party and is sufficient for my intended general observing - that is picking one or constellations on side of the sky during a night's session. I felt that further minimization of cone error could be achieved. The source of the remaining error seems be divided between play in the focuser locking set screw, inherent tube flexure and mount flexure. I'll probably buy a compression ring for the focuser for the heck of it, but for now pointing errors seem to be minimized to a level sufficient for my intended purpose, so I'll live with the rest of the cone error as is. So for now, its on to polar drift alignment, tracking images and tweaking the dec and ra motor speeds. In summary for an Orion 10" Newt (35-40lbs) and a Syntax EQ6 (Orion Atlas branded), cone error was excessive for the out-of-the-box model. Slews under hand-paddle control beyond 20-30 degrees resulted in the pointing errors that exceeded an average 1 deg TFOV e.p. view. The following modifications reduced cone error to 0 arcmins at RA0h, 0 arcmins at RA18h, and 1.5 arcmins at the RA6h position: 1) The primary source of error was flexible in the stock Orion aluminum extruded mounting bar. Subsituting a 12" LX-55 solid bar from Scope stuff was not sufficient to adequately control flexure in 10" Newt (35lbs) but was sufficient to control flexure in a lighter 5 1/4" (20-25lb) refractor. An extra-heavy duty extra-length (16") Ken Dauzet solid mounting bar was purchased. Although expensive, this brought flexure under control to the tolerance discussed above. 2) The Synta and Orion instructions for reducing perpendicular error, if implemented as written, consistently resulted in the center of field at the RA0h park position to be below the centering target. To address this, the instruction procedure was modified as follows. Cone error was minimized using the instruction proceedure. With the scope at the RA0h position centered below the alignmnet target (either Polaris or a small bush 3 kilometers away on a mountain). 1/2 the cone error was reintroduced using the alignmnet bolts thus raising the center of field near the alignment target. Then, the L-latitude bolts were used to raise the center of field about 5 arcminutes above the alignment target. The perpendicular or cone error procedure in the instructions was repeated a second time. This on the second run, the center of the field of view again lowered, but this time ended up aligned to the alignment target and with the cone error minimized. 3) This scope has been previously upgraded to a Moonlight Crayford focuser, so the degree of cone error that might be attributed to the low-end stock Orion focuser could not be determined. - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net