Suitable ADU range for Flats - ASI2600MC

starvoyager

Please advise a suitable ADU range ( black point to white point ) on the Histogram for good Flat frames captured with the ZWOASI2600MC

I realise this camera has a 16bit ADU (0 to 65,536 ADU )

I realise too generally Flats should be 1/3 to 1/2 along the Histogram

So therefore a target ADU should be around 32,000 ADU

But what is a good ADU range on the Histogram for good Flats ( Left side black point to Right side white point)
Lately my Flats have a ADU range on the Histogram of say 8,900 to 38,500 so am I over correcting
Should my ADU range be say 4,500 to 31,500

My set up
6” f6 GSO newt and 8” f5 GSO newt
Huon LED dimmable flat panel
White T Shirt and elastic band
Capture software APT ( CCD Flats Aid )
ZWOASI2600MC set in Ascom to highest dynamic range Gain 0 cooled to -10C
I usually calibrate my Flats with Bias ( I don’t take darks as they make no difference to my images ) I’ve tried Dark Flats but Bias work better

Any advice on the above would be appreciated
Thanks

wvreeven

starvoyager I realise too generally Flats should be 1/3 to 1/2 along the Histogram

Many people cling to that without an explanation. Not sure who first came up with that "rule" but I usually don't follow it.

The dynamic range of a picture increases with higher ADU values. So I generally aim for 55000 or more AS LONG AS THE HISTOGRAM DOESN'T GET CLIPPED ON THE RIGHT. This is difficult to establish sometimes because of hot pixels.

In any case, do NOT rely on flat wizards that help you to establish the "correct" exposure time. Do this be hand because it is much more precise.

And don't get obsessed by getting the optimum value. Some high average value is more than good enough. If you get good results with 32000 then that is good enough. Higher values may improve the SNR of the calibrated images, especially at the edges and in the corners but the difference will not be large, especially if there is a lot of vignetting.

elpajare

More about the subject; Asiair Pro has an automatic system to calculate the exposure and take the flats. Very simple and with good results.

wvreeven

elpajare Like I wrote (which was entirely on topic): don't use that. A manual approach takes more time and effort but yields much better results if only because you decide yourself what target ADU your flats should have.

elpajare

Well, you'd be amazed with the "illegal" things that we at EAA do. This is one of them!
This is the essence of EAA, observing celestial objects in an electronically enhanced way, and we can become very tolerant of the rules.

wvreeven

I'm not saying it's illegal. I'm merely saying that you shouldn't depend on wizards like this if you want to get the most out of your pictures. It's up to you what you do with that well meant advise.

starvoyager

Thanks for your comments and I’m aware that Flats are not automatic set and forget or a one shoe fits all scenario but I was hoping that someone has a 2600MC and could share some personal experience taking Flats with this particular camera both with and without Duoband narrowband filters like my L Extreme

wvreeven

I use both an ASI2600MC and an ASI6200MM and have shared my experience with those cameras. Sorry for not mentioning that. What else do you want to know?

starvoyager

From my original post , since you use the 2600MC what is the ADU range of your Flats
You mentioned you aim for 55,000 ADU ( as long as your not clipping, however I use APT Flats Aid and the Histogram only visually displays a compressed version of the Histogram and an ADU range ( In numerals) lowest to highest , hence that’s why I mentioned recently my Flats have been in the ADU range of around 8,500 to 38,500
The APT histogram really needs a redesign and Ivo, the developer has received many requests from users to provide a full range Histogram.
I don’t really want to change software or run another software program just for this Histogram issue
Can you see where I’m coming from

Thanks

starvoyager

Using my 2600MC in APT , I set an ADU target of 22,000 ADU
which results in a histogram range of 8,900 to 32,500 and an exposure of 0.49 sec
The RGB peaks are usually 1/3 to 1/2 along the Histogram
I capture 40 Flats and 50 Bias which calibrate ok. The above is without any filters
Using an L Extreme filter exposures usually end up being around 5 to 7 sec
Flats are working well producing a nice flat field , mitigating Vignetting and eliminating dust donuts