How can I improve on this flat?

Michael Finan:
What's your light source? Seems to be a color gradient.

Light source is a 10" round LED light.  But it's most likely too far away, which I am guessing is why the vignetting is only on the right side.  I am now doing it over with an additional white cloth over not only the scope but also the light source.  That way I can bring it a lot closer and still aim for around a 5" exposure, assuming that gets me a histogram that looks acceptable.

The light color is very even, not sure why that's happening either... Trial and error...

@Jerry Gerber are your light frames showing the same vignette as your flats?

What I’ve found so far with respect to the coloring…I image with a Canon 6d(Ha) and the L-eNhance. The colors you’re getting are the result of the bandpasses on the filter. The blue pixels are registering the wavelength for Hb. That wavelength does not peak like Oiii does for green and Ha does for red. The Ha(red) and Oiii(green) have a higher peak in the bandpass. So you won’t have as much “blue” data to color balance the image. This is what makes processes like PCC and the new SPCC so important for filtered OSC cameras. But this won’t matter for flat calibration as flats are generally applied to a light frame without debayering either the flat or the light frame in the calibration process. Debayering is generally done after calibration and often time after cosmetic correction. The flat frame is simply attempting to achieve a balanced field illumination. So the software will subtract the bias and dark frames, and then divide the flat frames. Thus, removing vignetting and dust etc.

can you upload a light frame?

That is normal i was confusued at the beginning too with my color cam. Very important: use bias frames for calibration. I was always skeptical, but it was the reason why my flats overcorreced all the time. I did bias and they worked. I have the exact same color gradient with your camera. Even the bias image got it😅 very wiered but hey it works

Joseph Biscoe IV:
@Jerry Gerber are your light frames showing the same vignette as your flats?

What I’ve found so far with respect to the coloring…I image with a Canon 6d(Ha) and the L-eNhance. The colors you’re getting are the result of the bandpasses on the filter. The blue pixels are registering the wavelength for Hb. That wavelength does not peak like Oiii does for green and Ha does for red. The Ha(red) and Oiii(green) have a higher peak in the bandpass. So you won’t have as much “blue” data to color balance the image. This is what makes processes like PCC and the new SPCC so important for filtered OSC cameras. But this won’t matter for flat calibration as flats are generally applied to a light frame without debayering either the flat or the light frame in the calibration process. Debayering is generally done after calibration and often time after cosmetic correction. The flat frame is simply attempting to achieve a balanced field illumination. So the software will subtract the bias and dark frames, and then divide the flat frames. Thus, removing vignetting and dust etc.

can you upload a light frame?

Thanks Joseph for the explanation.  I don't have any light frames yet.  I am taking small steps and learning everything I want to learn in order--first night focusing and polar alignment, 2nd night autoguiding, and today, since it's cloudy and/or the seeing is very poor, I spent the day learning how to take bias, darks, flats and dark flats.  I'm trying to be methodical so that I don't take any short-cuts.  There are no short cuts in life or art!

Joseph Biscoe IV:
@Jerry Gerber of course you’re right, no short cuts. Ok, so since you haven’t shot lights before with this equipment. You will see the same vignetting in your light frames. I’m not sure why, obviously I can’t see your imaging train, but I wonder if maybe there is some tilt at the sensor? You wont be able to be desire of this until you take light frames and not the Star shape in the corners. But I’m guessing there may be some tilt on the right side and that’s the reason for the light fall off.

Esprit 100 , ASI2600MC, AM5 mount, Pixinsight, Star Tools, ASI studio, ACD Ultimate (better than Photoshop and much less expensive)..

I think the vignetting is better in my 2nd attempt as I moved light source closer to telescope.

@Jerry Gerber ah ok, nice rig to start with! Yes the second flat’s vignette looks more normal. So you probably are good to go! ! 

calibration frames=trial and error until you zero in on your specific equipment. 

Can’t wait to see the end results you get

LED light - assuming they are like this one are completely fine for taking flats. I have used one for years. If the light panel cannot be dimmed enough, a good practice is to add a couple of sheets of white paper on top. This has the added benefit of acting as a diffuser and improving uniformity. You need to make sure that the panel, with diffuser if any, completely covers the field of view of the scope. The way I use is to have the scope pointed vertically up, then place the panel on top of the dew shield making sure atleast some lit part is seen outside the dew  shield on all sides. The flat used for calibration must have the flat dark subtracted from it (or the bias of you are confident enough that you can get a proper bias from your camera). And yes, calibration should be done before debayering.

@Jerry Gerber sky flats are great and pretty easy to acquire. 👍🏽

andrea tasselli:

Joseph Biscoe IV:
@Jerry Gerber sky flats are great and pretty easy to acquire. 👍🏽

Except in winter when is always dull and rainy and crappy all around, ly. Otherwise I'd wholeheartedly agree.

Of course you’re right haha!