Calibration frames applied 'inappropriately"

[alinderbaum]

Good morning - In addition to capturing light images, I was able to capture all calibration frames last night using Sharpcap for the first time. I noticed during capture that when each calibration frame (darks, bias, flats and dark flats) was saved, it was not saved as its own 'captured image'. Rather, when I opened up the FITs file, they appeared to have been applied to a light frame as they had stars in them.

The histograms looked very good and how they have always looked in the past for me, it just seems they were not saved as an individual calibration frame. I studies the settings (no live stacking) and have not been able to identify what may have happened or how to correct it. Any thoughts?

For a point of reference, in the past with I had used APT and the frames were each saved individually without being applied so when I opened up the RAW files, there was not a hint of the light frame being applied.

Thanks so much.

[admin]

Hi,

Could you share one or two of the frames for me to look at please? They will be too big to attach to the forums most likely, the easiest thing is probably to upload them to a sharing website like dropbox or Google Drive and then share a link to download them.


Thanks, Robin

[alinderbaum]

Robin,

Sure. Below is the link to one of the dark frames and other related 2 files. Thank you.


https://1drv.ms/u/s!AhE2Rt0-5SmlgVn88zn ... 5?e=omGeun

[alinderbaum]

Robin,

I think I may have uncovered the issue. I have gone from a DSLR to an Altair 269C camera. With the DSLR I never saw anything in the dark images, just blacck. With the 269C, could it be that it is picking up things (specs of various sources) that the DSLR may not identify? I looked at these dark images again and think the specs I see were not stars but rather noise. The noise, unfortunately, looked very much like the pattern of stars in NGC 6888. I think I may have just been thrown off on that. Does that sound reasonable?

Last night I tried to stop a capture sequence by hitting the "X" on the notification bar after hitting stop capture. I could not get the capture sequence to stop. I looked in the manual and it said to stop it by hitting the X on the notification bar...unless I am misidentifying the notification bar.

Many thanks for all of your support! The Polar Alignment is getting easier and helping me track wonderfully and I am not using my guide scope yet.

Aaron

[admin]

Hi Aaron,

Yes, I agree that the bright dots in that image look like hot pixels against a low-level background of noise. It may be that the DSLR camera uses some software tricks to try to eliminate things like hot pixels ( there was a time when Nikon cameras did this rather enthusiastically and would happily take out pretty much every star in an image!).

If you are running a sequence of captures and you press the stop capture button then it will start waiting for the next capture in the sequence. Pressing the X button just dismisses the message – you should look further left and you should see two buttons that are labelled 'don't wait' and 'Cancel' – it's that cancel button that you want to stop the whole sequence.

Glad to hear that the polar alignment works nicely for you

Cheers, Robin

[alinderbaum]

Robin,

I will do that. My recollection from last night is that the Don't Wait and Cancel buttons did not come up in the notification bar...only the file location where the files were being sent to (the capture file). I will test again in case I overlooked them last night.

[alinderbaum]

Robin (and all) - Below is a link to one image each of NGC 6888 (light, dark, flat, dark flat and bias). Due to an oversite, the gain on a couple are slightly off from the others, but not enough to cause the strange, significant, oval pattern that Is in the light frames from the Altair 269C.

https://1drv.ms/u/s!AhE2Rt0-5SmlgXK04hZ ... I?e=6Sd0lS

I used the flats capture in Sharpcap and it appears to be solid. I have never seen anything that was not removed through calibration with my DSLR so this is a new one for me. I appreciate any insight that can be shared.

Aaron

[admin]

Hi,

So two things jumped out at me while looking at the frames that you shared. Firstly the light frame was showing the very odd lozenge pattern in the centre – I wasn't clear whether this was a pure light frame or it has correction applied to it. If it's a pure light frame then the problem is nothing to do with dark or flat correction. One thing that does occur to me is that it might possibly be frost or dew on the sensor creating that pattern on the light frame.

The other thing I noticed was that you are using a colour flat frame – it would probably be better to check the box in the flat frame creation tool to create a monochrome flat frame. Colour flats can work well under some conditions to correct colour balance as well as performing flat frame correction, but the differences in brightness between your colour channels are really too big for it to work well in your case. One of the colours is close to minimum saturation and the other two are getting close to maximum.


Hope this helps, Robin