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I cannot get my flat frames to work

Canon EOS 6D DSLR Acquisition Calibration Deep Sky
8 replies•339 views
Menelaos avatar
Menelaos avatar
Hi guys,

I’m making a topic again for flat frames.
i am using a dslr (canon 6d) and i’ve been experimenting with flat frames because i was never able to get them to work. I’ve tried everything that i was reading online and all recommendations from other astrophotographers. I’m using a white panel with a tshirt, i tried the histogram from all the way to the left to all the way to the right, i’ve tried exposure times from just below a second to 1, 2, 3 up to 10s. I tried using flat darks, bias, tried not using any of those and it makes no difference. I even measure the adu for my camera! Nothing worked! 😩 what am i doing wrong? Any ideas??
Engaging
andrea tasselli avatar
andrea tasselli avatar
The usual culprit to this predicament is that you have a light leak of some sorts. which is normally  quite difficult to give advice for because we aren't simply there with you. Given that you use a Newtonian the risk there is rather significant.
Menelaos avatar
Menelaos avatar
andrea tasselli:
The usual culprit to this predicament is that you have a light leak of some sorts. which is normally  quite difficult to give advice for because we aren't simply there with you. Given that you use a Newtonian the risk there is rather significant.

If i’m not mistaken the light leak will introduce uneven illumination in certain areas of the image therefore inaccurate corrections. Am I correct? In my case it either overcorrects or does nothing at all. The closests i got to correcting the image was when i used a histogram matching the light frames and even then it was not good enough.
Oskari Nikkinen avatar
Oskari Nikkinen avatar
Can you post an example image of what your calibrated subs look like when the flats dont work? Simple stretched JPEG will work for that use.
andrea tasselli avatar
andrea tasselli avatar
If i’m not mistaken the light leak will introduce uneven illumination in certain areas of the image therefore inaccurate corrections. Am I correct? In my case it either overcorrects or does nothing at all. The closests i got to correcting the image was when i used a histogram matching the light frames and even then it was not good enough.


Indeed you are, a light "leak" can take many different shapes, Overcorrection is a typical example of the effect a light leak has on the flat normalization operation.
Jeffery Richards avatar
Jeffery Richards avatar
An autostretched image of the flat would be helpful as well. I find using NINA flat wizard to be most helpful in getting the correct exposures for my flats.
Well Written Concise
Menelaos avatar
Menelaos avatar
Jeffery Richards:
An autostretched image of the flat would be helpful as well. I find using NINA flat wizard to be most helpful in getting the correct exposures for my flats.

i’m using an asi air is there an equivalent to NINA?
Jeffery Richards avatar
Jeffery Richards avatar
Ahhh, then NINA won't work for you. But providing an autostretched flat would still be useful so we could see what it looks like. Also a light processed with and without your flat as well.
Elmiko avatar
Elmiko avatar
You're flats should have a reading between 25000-30000 adu. Just adjust the exposure time to achieve that.
Mike
Concise