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Hi Ken,
No. It is not a Dec issue. When adjusting for cone angle, moving the dec serves no purpose except to bring the target star to the middle of the RA target line for viewing.
With the scope at TDC, I try to bring the target star to the centre of view. I do this with two adjustments. The critical one is by physically shimming the OTA to point up, or down as required to bring the target to the middle height of view. (Trying to make the line of the OTA exactly parallel with the axis of rotation of the mount. Dec adjustment aligns the LR direction, shimming aligns the up down)
The dec is only adjusted to bring the star left or right into the field of view.
When rotating the mount 90°, the effect of shimming now affects the apparent L-R position of the target star.
What I expect to see when I rotate the mount to -say the right, is the target star appearing a little to the right of centre, and when I then rotate the mount to the left, I see the target appearing also to the right. The difference between the two positions needs to be adjusted with shimming so the L and R become the same.
Then, ideally, with the target star aligned through the polar scope to be in the centre of rotation, through the OTA, the target star should also appear to be be in the centre (with appropriate dec adjustments) regardless of the angular position of the mount. TDC, left 90 or right 90, and everywhere between.
Hope this makes sense.
Cheers Brian
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