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"images of short exposures at high ISO images seem to be better than the equivalent shots using lower ISO and longer exposures" That's an attribute of CMOS technology - low gain readout incurs less

" changed to an OAG because ... I am lazy" That's the usual rationale I hear from piggy-backers. <g> I predict that in the not distant future, guiding will obsolete; similar to the illuminated reticle

I have heard that it is possible, and there are programs out there,?to model the tracking error and reasonably track thereby. My own testing indicated the error?might be?reliably consistent, but I

My only experience has been that when I once tried to really make sure the locking ring on the secondary was screwed on?secure and tight, the whole corrector plate began to turn. Based on that, I'd

I have been guiding a C14 EdgeHD with a 1000ml fl f10 guide scope successfully for a few years. I use PHD and there is a learning curve but once the settings are derived, it guides well. I changed to

I have recently attempted to precisely center my corrector plate based on issues brought up discussing HyperStar alignment. I used a Hotech advanced alignment tool. I noted that my secondary shadow is

Thanks for the update and info, The development of the CMOS sensors has been impressive. Your post has inspired me to try again with just the idea of more short exposures at higher ISO ratings. I have

Thanks for the update, I was following this thread too.

nicely de-bugged. Stan

Just wanted to update everyone on the status of my problem. Looks like it was a slight field rotation. I would see it on some frames and not on others because of the location in the sky, guide cam

I tried to access the document via link - it's protected. The one that's downloaded in the archives has no appendix. I'd love to get more information on the issue. If possible, let me know how to

Read the appendix starting on page 8 of the document linked below. I probably uploaded it into the archives too. Internal dew heater with appendix on mirror shift

" I don't pay any attention what's my last turn." It's possible that is the source of the problem. The notorious "SCT mirror shift" moves the optical axis by the same amount as the image offset. So it

"watching the actual graph many times to figure out what's going on" Not sure that is adequate, though it might be the only feedback from your guiding software. I like to watch the actual guide

Stan, Do you mean to say that the locks will not prevent mirror settling even when locked down? And have to confess - I don't pay any attention what's my last turn. I gather it would have to be

Stan, Thank you for all the suggestions. I think my guiding is fine. I've been watching the actual graph many times to figure out what's going on. Aberration is always on a part of the frame, which

"to always lock-down the primary when imaging" Also - be sure to always focus against gravity (the last turn). Otherwise the mirror will re-settle during the exposure.

It is definitely worth spending some time debugging via very short exps. Next time you download a defective image, take some short exps to see if the defect is present at small time frames or is a

I am OAG guiding. My guiding is within 0.2-0.3 arc-sec RMS error (at least during the time I took these frames). If it were some kind of a differential flexture would't it show across the whole frame?

or maybe not. The frame is too small to fully judge. How do you know that "guiding is good"? If it is not guiding (and I still think that is a likely culprit) then it might be internal flexure that