Flats Help! I'm at my wits' end...

[FacelessMan]

Good day!  I've been having a lot of trouble with flat frames.  Like a lot of trouble.  No matter what I do, I can't seem to get them to work.  I've tried a bunch of different ways of calibration (with darks, without darks, with bias, without bias, with flat darks, without flat darks) and they have NEVER worked.  I've tried different file formats, programs, everything.  They either overcorrect, or undercorrect. 

Here is a link to a dropbox with a flat, flat dark, and light.

https://www.dropbox.com/sh/mmy0f1i0gexgjgg/AABReKlQjCIxcpm9K7qyZmm5a?dl=0

I use a modified Nikon D5300.

[Stu]

Hi, and welcome to the forum.

I’ve hidden your two other identical posts so that all the answers go onto this thread, should be much easier.

thanks,

Stu

[wornish]

What software have you used to do the integration ?

[david_taurus83]

How have you ended up with tiff files? Are you calibrating with the raw nef files before debayering?

[FacelessMan]

I used Pixinsight to integrate.  I've tried before with all frames with both .fits and .NEF extensions, but it doesn't make a difference.  I converted them to tiffs so everyone could see them/view them.  I'll post the raw fits in the link as well.  I calibrated the flats with  flat darks, and then the light with the flat.  I calibrated the lights with darks as well, but it doesn't help either.  All of these images were taken within a couple hours of each other.  Thanks for the help!

[FacelessMan]

Thanks for deleting the identical topics.  After I posted the first one, I thought it would be a better fit for this forum.

[vlaiv]

11 hours ago, FacelessMan said:

I've tried a bunch of different ways of calibration (with darks, without darks, with bias, without bias, with flat darks, without flat darks) and they have NEVER worked.

In theory flat calibration will never work on camera that does not have set point cooling. Simple as that.

You can get it good enough so that you don't notice it's not working well. But that is about all you can do.

Closest to getting it to work would be this:

- shoot bias

- shoot darks (aim to actual ambient temperature lights were shot at)

- make sure you don't have any light leaks when doing darks (or any subs with covered scope - flat darks and bias included)

- shoot flats - make sure you are not clipping them

- shoot flat darks

Calibrate with dark optimization turned on. For this to work, your camera has to have stable bias. Let's hope it does.

You need bias for dark optimization and you need dark optimization because you really want your darks to match your lights. Any temperature change will either add or subtract some signal from calibrated sub (either more dark current or less dark current). When you divide with flats - that creates either over or under correction - because you have some signal that did not come thru lens and is not influenced by flat field but you are trying to correct it with flats.

For flats to work properly, only signal that is corrected needs to be light that came down telescope tube - so no light leaks, no residual dark current - nothing, just pure "vignetted" light signal.

 

[FacelessMan]

Thank you!  I've been using a PixelMath formula to recorrect the final stack with the Master Flat.  I also generate synthetic flats and process with those.  It's a PITA though.  I am using SGP's Flats calibration wizard, but I'm not fully sure if it is working.