QHY268M correction issues with camer in pixinsight

Calibration Help Needed
11 replies•244 views
RammaN avatar
RammaN avatar
I have had this camer for a couple of months and I have not been able to properly correct images. I am coming from a 294mm and mc and I am using 33 darks at matching temp and 33 flats at matching temp. flats are calibrated with flat darks. Images are processed andually and with WBPP with the same correction issue. 
I have hit a brick wall with this issue and I would like to figure out what I am doing wrong. I have used the camera with a hyperstar and with a starizona sct iv reducer.

(top) uncalibrated single sub (bottom) calibrated stack with flats and darks in WBPP.

I can answer any other questions that you might have. I would like to get this issue figured out
Thank You for any help!
RammaN avatar
RammaN avatar

masterflat 30000adu, created with NINA flat wizard
Brian Puhl avatar
Brian Puhl avatar
You shouldn't really need darks, but did you use bias or darkflats?

edit: sorry i see you said flat darks in the first post.    What are the exposure times of your darkflat or bias frames?
Sean Mc avatar
Sean Mc avatar
Are you just using flats and darks?  How a bout bias?
RammaN avatar
RammaN avatar
My flats are 1.12 seconds and they are calibrated with a flat dark of 1.12 seconds then stacked into a master either manuall or with wbpp. When manually stacking i select averaging, multiplicative and equalize fluxes. Wbpp i just lock the flat darks to the flats and then the darks and masterflat to the lights.
RammaN avatar
RammaN avatar
Its odd to me beacause i am processing the same way i would with my 294 mm/mc cameras but the correction is all wrong.
Im almost to the point where im assuming light pollution is the issue as i cannot figure out the calibration. I would assume though that would show up in the idividual frames, wich it does not look like it is at f7, the hyperstar at f1.9 has the same issue.
RammaN avatar
RammaN avatar
Should i just be using a bias frame with this camera?
Brian Puhl avatar
Brian Puhl avatar
Should i just be using a bias frame with this camera?



I've never used darkflats personally, only bias and flats.    darkflats shouldn't be much different.    I saw this issue once when I had issues with my bias exposures.   I forget the exact reason, but I had a bit of vignette i remember.    Chances are your darkflats might exhibit this behavior if you look at them in Pix.

Try bias frames tho, nice really short exposures.    Then try adding a pedestal to your WBPP process.   It could be oversubtracting.
andrea tasselli avatar
andrea tasselli avatar
This normally occurs whenever you use a double subtraction or you forgot to remove bias from lights/flats or darks weren't used whenever they should.

So, to summarize:

1. for master flat use darkflats of the same duration, gain and pedestal of the flats.
2. for master darks do no subtract anything, just stack them up.
3. for light frames calibration use only the master dark at point 2 above and the master flat at point 1 above.

Don't use WBPP. Do it manually.
Miran Brezočnik avatar
Miran Brezočnik avatar
Should i just be using a bias frame with this camera?

The solution to this issue is very simple. You need to create a set of bias frames (e.g., at least 30) so that the flat frames will work. I have the same camera as you. Without bias frames, flat frames won't work. With this camera, I only use bias and flat frames, and it works like a charm.
RammaN avatar
RammaN avatar
Thank you all i will definitely try these suggestions!!
RammaN avatar
RammaN avatar

thank you everyone for the help!!!
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