Please help with statistics

I like to get some statistics on SCT focusing image shift. How is your scope? Instead of just "good" or "bad," how good or how bad is it in arc minutes or arc seconds? I guess for completeness we should know Meade, Celestron, or "other" and what size scope it is. Maybe with enough responses we can quantify some of the Celestron/Meade discussions I have seen here. I hope this thread will be useful to others on this forum and not just something to satisfy my curiosity.

To get things started, I have a 16" Meade showing (at latest test) 3 minutes of shift. For those who followed a previous thread this shift got significantly better after lots of focuser "exercise" by moving through its whole range several times. I'll post results for other local scopes I know of as I get the information.

Thanks,
Charlie

Charles…

I have a Celestron C5+ (admitedly much smaller than your 16"). Image shift is essentially zero.

At one time or another, I have looked through one or more 5", 8", 9.25", 11", and 14" Celestrons and 8", 10", 14" and 16" Meades (no 12" yet). My sampling is far too small to be scientific, but my experience is that the smaller scopes generally have less image shift than the larger scopes. One exception to this trend is a Nexstar 11 (just moved with its owner to Arizona) that had only the very slightest image shift and a couple of scopes of both brands that have been "worked on" to virtually eliminate image shift.

I strongly suspect the weight of the primary mirror is the main culprit in this trend…the focusing mechanisms may not be scaled up as well as they could be. Size for size, the Celestrons have been a bit better than the Meades with respect to image shift, but not always so.

Fred