CCDInspector Confusion

[Freff]

Last night I attempted real-time collimation. As instructed I adjusted the secondary screws in the direction of the indicator. Alls well, the number came down and I stopped at 0.6" from 20" when I started. great I thought. I left well alone and just continued to take the images and watch the indicator remain static.

Not so, the indicator varied anywhere from 18"-1" with each image as it was processed. The scope remained on the same star field and tracking I wouldn't have thought would have mattered as the exposures were only 30sec. I am totally confussed and a bit disappointed.

Looking at the results from CCDinspector, it appears the numbers shown here dont correspond with the colours. The scope had been outside for 2hrs so plenty of cool down time.

If anyone can help out I'd been very grateful. Many thanks.

[MG1]

I'm just starting to play with CCDi so I may not have all the answers you're looking for, but I do know that the colours reflect the field curvature not the collimation.

Did you lock everything down at the end? there may be some flop in your focuser maybe? Also if you read these figures in conjunction with the FWHM you will get an idea as to what the seeing is doing and if that has had much effect.

Although it has appeared clear over the past few days for me, the high level smog/mist/cloud/ particulate matter has made doing anything difficult.

Have a read of the CCDi readme/help file and this explains how FWHM relates to seeing far better than I can.

I only really have data for my setup and I'm reaching a flatness of around 7% across a 35mm chip using a dedicated field flattener...but my colimation is still not perfect, being around .1" out...not much though I would like it to be spot on.

All I can suggest is collect multiple frames for each time to tweak it and the average the results....

And include darks so that it isn't callibrating against any hot pixels.

Sorry if that's not much help....as I said, I'm still learning this dark art!

I'm sure an expert will come along soon

Michael

[Freff]

Thanks Michael sorry for the late reply.

I appreciate the collimation and colours are separate issues. I just couldn't get my head around the collimation figures being so different after each capture. No adjustments made for 5 captures (30sec) yet the readings were vastly different.

I think I will try and digest the instructions more so I can interpret the results.

[Paxo]

You may need a richer star field (or longer exposures) to get the best out of the real-time collimation as CCDi uses star shape and FWHM to assess the degree of collimation.

Steve