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Old 23-07-2018, 08:48 AM
ericwbenson (Eric)
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ericwbenson is offline
 
Join Date: Sep 2009
Location: Adelaide, Australia
Posts: 209
Hi Peter,

More to chew on...
Assuming your scope has an EFL=1260mm (180mm f/7 correct?)
Your plate scale is = 206225 / efl = 163.7 "/mm

Taking your stated eccentricity of 5' = 300" and dividing by the plate scale and you get ~2mm (assuming you meant diameter?). If the CCD sensor is offset by 1mm from the rotator mechanical axis for whatever reason that would explain the rotating stars around the sensor center.

This can come from a combination of (in order of importance IMO)
a) the camera itself (mounting aperture/holes not centered - direct offset)
b) the rotator bearing itself - this can be checked with a laser.
c) the adapter from rotator to camera sitting crooked on the rotator side.

a) is difficult if not impossible to verify precisely (you are not going to open the CCD chamber for this!!!).

To check for b). First ensure the laser is aligned to it's holder (rotate manually in a v-groove at observe the beam orbit on a screen a few meters away) Then if possible rotate the holder in the rotator manually while observing the distant orbit (a helper here would be good) to get a baseline for measurement uncertainty. Next operate the rotator motor to measure it's wobble.

The angle at which the adapter is sitting is = the contributing offset divided by the adapter thickness. For example if the adapter is 10 mm thick, and c) is solely responsible with offset = 1 mm, the angle is 1/10 radians = 100 mrad ~ 6 degrees. You would definitely pick this adapter as looking crooking.

Later,
EB


Looks like our posts crossed, I'll get back to you later...

Last edited by ericwbenson; 23-07-2018 at 09:00 AM.
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