Please help me get photometric colour calibration on this image

Hello. This is the FITS file I’m having trouble with

That file is the final stacked image. I have done nothing to it yet.

It’s a shot of the Orion constellation at 18mm (plus 1.6x crop factor) captured with my Canon EOS 1100D (untracked) with 3200 ISO and 10s sub-exposures (~500 lights).

The photometric colour calibration (PCC) tool keeps failing and I have tried several things but all failed -

  1. Changed the focal length to 28mm in the PCC tool.
  2. Manual star selection
  3. Uploaded the file to nova.astrometry, copied the RA and Dec and pasted them in the PCC tool.
  4. Crop before PCC.

I could do manual color calibration but it’s not giving me very good results.




Image taken at 18mm are very distorted. This is why it is very difficult to platesolve this kind of image.
Also, even if platesolve was possible, imagine than you only have 3 or 4 pixels for a star. That means that photometry cannot be accurat.

In addition, your image presents a huge vignetted inverted. That means that your calibration is wrong. Photometry needs a flat image to give good results.

What do you mean by “huge vignetted inverted”?

I meant inverted vignetting:

Ah yes. I’m guessing my master flat is over-correcting?

It is generally a bias issue: Siril - Synthetic biases

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Thank you!
Read through it. I think it’s because I shot dark-flats instead of biases. Will try with biases.