Hey Paul,

In a perfect world we would have consecutive nights of great seeing, no wind, cool temperatures, etc. with which we could do all things "astronomic". To say that's not the case in south Texas right now would be an extreme understatement. My question: what effect if any would mediocre seeing have on making collimation runs on my RC? FocusMax gives me tight focus and I have a stable mount with which to image. I'll be using an SBIG STL-11000 with an image scale of 1 arcsec/pix.

Thanks.

Ron

Hi Ron,

What's the average HFD or FWHM you see after a good focusing run? How variable is it on consecutive, short-exposure frames?

Collimation is easier and better done on a night of good seeing. With the single-star defocused method in CCDInspector, you will be able to tell when you've come to the limit of what's possible for that night. The direction of the error pointer will start shifting randomly in all directions with each exposure.

You can still achieve a reasonable collimation when the seeing is not good, but in a really poor seeing, I wouldn't recommend trying. Maybe an artificial star would be a better choice for such nights (and would work just fine with the defocused star collimator in CCDI).

Regards,

-Paul

Hi Paul - thanks for the quick response. I'm using a new system setup and have only taken a couple of test images. They were 10 minutes and 15 minutes in length and the FWHM came in at 2.4-2.6 under fair seeing. So I'll have to shoot some short focus frames to answer your question precisely. You did answered my basic question regarding the decision to collimate with marginal seeing and I appreciate it. I'll check back in if I get a chance to image/collimate this weekend.

Ron

Hi Ron,

A long exposure of 2.4-2.6 arcsecs is just about average, I'd say. I wouldn't call it really bad seeing -- that would be in the 4-6 arcsecs FWHM range

I think you should be able to collimate pretty well if the seeing holds up in the range you are quoting.

Regards,

-Paul

Thanks Paul. I was wondering if there was a FWHM "zone" that would be appropriate to collimate within. If I get a <=2.5 arcsecs night this weekend I'll give it a shot.

Thanks again.

Ron