Horizontal Lines/Bands in Image

[GeneralT001]

Hi,

Took some images of M31 last night and after stacking (in Pixinsight) I auto stretched to have a look and I see these lines in the image.

The camera is an ASI1600MC-Cooled. I took flats/darks/bias frames.



My calibration frames were shot as follows:
 
•Flats .27 sec exposures using a spike a field
•Darks 45 sec exposures
•Bias 0.0 sec (SGP)

Camera was cooled to -20c for all imaging/calibration files.
I used all this the other night and the image seemed to come out fine with processing in Pixinsight?

I don't want to further process this until I know whats causing this.

[jkmorse]

It would help in assessing the problem to look at the individual stacks.  Where is this pattern coming from?  Also, what were your settings in Image Calibration?  You may be doubling up corrections from both the Bias and the Dark which may be part of the issue.  Also, something is going on with your flats creating the strange dark and light sections in the processed image.  What does the flat alone look like?

[GeneralT001]

Hi,

Here are links to the Flat file and the Stacked .xisf file.

https://www.dropbox.com/s/r26w3rws9b7xn3e/Master_Flat.xisf?dl=0

https://www.dropbox.com/s/gbx0fmuyi6uebp5/M31_Andromeda_No_Drizzle.xisf?dl=0

I followed the tut on HarrysAstroShed about preprocessing. I used it just yesterday and all seemed to work out fine.

[vicent_peris]

Hi,

I didn't download your images, but I would recommend you to load all the images in Blink to see if there is any problematic frame.

Best regards,
Vicent.

[GeneralT001]

Hi,

I'm new to Pixinsight and didn't even know about Blink. I love it, as I have been looking for a .Fit file viewer for image assessment. Worked like a charm. My subs were all good.

I tried doing some trouble shooting by just processing a small number of the files with/without various calibration frames. I think the problem may be the latest flats I shot with this imaging session. They were .3sec long were my previous flats were .08 sec. Not sure why that would make a difference (maybe this was caused by the light panel being too dim and interference lines were picked up?

I ran the subs through with a set of Flats from a previous night (.08 sec) and the integrated stack looked normal (I think). Won't be 100% sure until I finish a complete stack with all Bias/Dark/Flat frames included.

[vicent_peris]

Hi,

Sorry, I meant to review in Blink all the images including the calibration frames as well, not only the lights. Load separately all the flats and review them, then the darks and then the bias. I recommend you, each time you load a set of images, to adjust the histograms in the Blink tool. You'll find this option as a little histogram button just left of the image list.

It's extremely important to review and inspect all your data sets before start preprocessing. All these problems arise many times from silly mistakes (imagine what could happen if one of your bias is classified in the FITS header as a flat image...). I recommend to put Blink in your favorite list in the Process Explorer.


Best regards,
Vicent.

[GeneralT001]

Will definitely do. 

Thanks

[pfile]

does that sensor have an electronic shutter?

the flats are awfully short - with some types of mechanical shutters, short exposures can leave shutter artifacts. also because of the way electronic shutters work, i think short exposures could cause problems as well. the flat panels do "flicker" at around 20khz or so.

you can try putting a bunch of sheets of white paper in front of the flat panel to dim the light down and allow longer shutter speeds.

rob