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Circular Bands in Flat Frames

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#1 Adas

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Posted 25 September 2021 - 08:39 PM

Hello all.

 

I just got a Spike-a-Flat and tried to shoot a few flat frames with my Ha filter on my ASI2600MM and RASA11.

The brightness on the panel was set to 20 (range: 0-1023).

Camera gain 0, Offset 50.

I used SGP's Flat calibration wizard to arrive upon an exposure time of 5.76 secs, yielding a mean ADU of 29,900. 

See some circular banding in my flats.

Any ideas where the problem could lie?

Attaching the flat file autostretched in PI.

Thanks!

 

 

flat_pi_sample.JPG


Edited by Adas, 26 September 2021 - 12:32 AM.


#2 Oort Cloud

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Posted 25 September 2021 - 09:58 PM

I don't have a RASA, bit I always wondered about taking flats with one. Since the camera is all up in the way, I assumed you'd have to do sky flats. My guess would me reflections from the side of the camera, since the light source is so close.

So I guess the real question is: Do the flats work?

#3 Adas

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Posted 25 September 2021 - 10:35 PM

Thanks for your response!

That sounds logical. 

I'll calibrate the Ha image and let you know.

BTW, just took some flats with O3.

Everything same except exposure which is 6.28 sec.

This does not show such gradient.

 

flat_pi_sample_O3.JPG



#4 Adas

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Posted 26 September 2021 - 12:38 AM

Here are my Ha images stacked and stretched in PI, Calibrated and not. No other calibration frame used other than flats.

 

 

flat_pi_sample_Ha_comp.JPG

 




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