Nebulosity, darks, temp... question
Posted 08 January 2013 - 05:30 PM
A few nights ago I tried to image the Horsehead nebula. In Nebulosity I set the TEC to -15 C. (I was working under the the assumption that Nebulosity is reporting the CCD's actual temperature, rather than a temp relative to ambient or something.)
It was late so I decided to take my darks the next morning, indoors.
The lights (Ha) look as I would have expected – reasonable data and a lot of noise.
My stack of darks look reasonable to me too. However when I pre-process my individual lights with the dark stack the result seems to show no nebulosity at all. In fact there appears to be not much appart from a couple very bright stars. Certainly no DSO detail.
What might I be doing wrong?
Posted 08 January 2013 - 05:54 PM
Apply DDP, or levels/curves and the nebulosity will be there.
Posted 08 January 2013 - 07:05 PM
The pre-stretched histogram doesn't look good at all – there's no data in the mid tones... or high lights either, for that matter. It's all clipped at the shadow end. Stretching produces no image.
If, however, I stack the the lights without applying the darks I can stretch out a fine image (although there are bad pixel stacking artifacts everywhere.)
Posted 08 January 2013 - 07:36 PM
If this works, that means Nebulosity does not auto-stretch well enough with images containing very low ADUs. I had the same issue and it worked if you follow my instructions.
Posted 08 January 2013 - 07:54 PM
First of all that didn't seem to help. I'm pretty sure there's nothing there. I suspect I've done something wrong with my darks.
Perhaps you can help me fill a gap (one of many) in my understanding. Like I said, the lights – by themselves – seem to stretch out nice. I would have thought that the application of (appropriate) darks wouldn't affect the "good" part of the image data. No?
Posted 08 January 2013 - 08:49 PM
Posted 08 January 2013 - 10:17 PM
When I tried to calibrate the light with the dark, I got the same thing as yours. Then I calibrated using Bad Pixel Mapping from your dark, and it works and looks cleaner.
Posted 09 January 2013 - 11:18 AM
I tried shooting a few darks using CCDSoft and they look much better, with a min of 91. Applying those darks to the original image data doesn't work, of course, but does produce the results I would expect. I think now I will try to capture a set of lights with CCDSoft.
Does anyone else use Nebulosity for capture with an SBIG camera?
Posted 09 January 2013 - 11:23 AM
I use Nebulosity and it's a wonderful capture as well as processing software.