Flat Darks or Bias? - Forums

Hello,

I'm going to be using the Esprit 100 ED with the ZWO ASI2600MC camera, sitting on a ZWO AM5 mount.

I'm wondering whether I ought to take dark flats with my flats or forego the dark flats and take bias frames.

Anyone using this camera have any experience they'd like to share with me, or is this something I just need to experiment with?

Thanks!
Jerry
www.jerrygerber.com

I don't have experience with that camera, but with every other CMOS camera I have used, dark flats turn out equal to or better than bias at a total cost of a few extra seconds per set.

I dno't have the 2600 mc, but do use the 294 mc. I definitely recommend using equal time darks to the length of your flat frames. (aka dark flats) This will account for the baseline electrical/bias noise in the senor as well as any thermal noise present for the length of the flat frame. I use 6 sec flats using neural density film and flat panel. I have had to do this to calibrate out the banding on the 294 mc sensor especially at faster focal ratios less than F4. CS -Brandon

Best practice with several CMOS cameras (but not all) is to shoot dark-flats to go with flats.

Jerry Gerber:
Hello,

I'm going to be using the Esprit 100 ED with the ZWO ASI2600MC camera, sitting on a ZWO AM5 mount.

I'm wondering whether I ought to take dark flats with my flats or forego the dark flats and take bias frames.

Anyone using this camera have any experience they'd like to share with me, or is this something I just need to experiment with?

Thanks!
Jerry
www.jerrygerber.com

With current generation of CMOS cameras, BIAS work well. My judgement is based on experience with three cameras (QHY600M, QHY268M and ASI 533MC all with the same CMOS technology as your ASI2600MC). Previous generation CMOS was a different story: I had the 183M that had amp-glow and there BIAS where non-reproducible. Only option were DARKFLATS. Hope that helps. CS, John

I have two 2600MC Pro's and use Flat darks with Flats and occasionally Darks only if I add older subs for which I have no Flat darks. Never Bias.

scott

It appears to me that either bias or flat darks will work. I'll have to experiment. Nothing beats direct experience!

Jerry Gerber:
It appears to me that either bias or flat darks will work. I'll have to experiment. Nothing beats direct experience!

You can experiment - or you can use fundamentals.

The flat-dark that you take, which is a dark with the same exposure time as your flat, already contains the bias signal. So there really isn't any downside to calibrating with a flat-dark. The only requirement for proper calibration with a flat-dark is that the flats be the same exposure time as the flat-dark. And this is especially easy with a color camera, since you dont need to worry about the complexity of filters. Just decide what ADU number you want to target, set your panel to the brightness required to get a desired exposure time (usually greater than 3 seconds) and it is the same every single time. So I guess I don't see the benefit of going with a bias for a color camera, especially given the known issues with some of them.

I personally use the 2600 MC. I calibrate using flat-darks. I've never used a bias for any of the CMOS cameras I've had (ASI1600MM, 294MM, 2600 MC).

I have the same setup (Esprit 100 / 2600MC). When I got the camera, I made some tests, with bias and without bias. There was no difference. Then I had dark-flat and got much better results !

Denis Labelle:
I have the same setup (Esprit 100 / 2600MC). When I got the camera, I made some tests, with bias and without bias. There was no difference. Then I had dark-flat and got much better results !

Would you mind sharing the 'much better results' that you got? Thx.

The consensus from those who actually have experience with the asi2600mc is that flat darks are the way to go. So that's the way Ill start. If through my own experience I find out something different then I will re-assess.

Thank you everyone for sharing your experience, much appreciated!

Jerry
www.jerrygerber.com

Very easy to test… take a bunch of bias frames any time. Then, next time you image, take flats and flat darks. Run through once using the bias and once using the flat darks. Evaluate.

Jerry Gerber:
Hello,

I'm going to be using the Esprit 100 ED with the ZWO ASI2600MC camera, sitting on a ZWO AM5 mount.

I'm wondering whether I ought to take dark flats with my flats or forego the dark flats and take bias frames.

Anyone using this camera have any experience they'd like to share with me, or is this something I just need to experiment with?

Thanks!
Jerry
www.jerrygerber.com

I have an Esprit 100ed, 2600mm Pro camera on an iOptron GEM45 mount… I have 2 large dust ‘bunnies’ somewhere inside the optics.
After imaging I take Flats and Flat Darks for each filter and stack the Flat Darks in Pixinsight under the Bias Tab…
I have totally clean sub frames using this method…
Hope that helps
CS Olly

I am using the 533MM and there is literally no difference between using bias or flat darks. I prefer to use bias because they are easier and faster to capture and the same master works with all the filters.

Jerry Gerber:
Hello,

I'm going to be using the Esprit 100 ED with the ZWO ASI2600MC camera, sitting on a ZWO AM5 mount.

I'm wondering whether I ought to take dark flats with my flats or forego the dark flats and take bias frames.

Anyone using this camera have any experience they'd like to share with me, or is this something I just need to experiment with?

Thanks!
Jerry
www.jerrygerber.com

I use the 2600MC (great camera!) with an Esprit too. I always shoot flat darks right after the flats. If you use NINA it's all automated for you.

But I also have a set of master biases (at the various binnings) just in case I find I don't have a matching exposure master dark for the lights. WBPP can then use the master bias to 'scale up' the dark to match. So for example I shot lights of 300s but I only have master darks in my library of 240s and 360s, I can use the 240s master dark and WBPP can adjust it with 'Optimize master dark' and the master bias.

Olly Barrett:
Jerry Gerber:
Hello,

I'm going to be using the Esprit 100 ED with the ZWO ASI2600MC camera, sitting on a ZWO AM5 mount.

I'm wondering whether I ought to take dark flats with my flats or forego the dark flats and take bias frames.

Anyone using this camera have any experience they'd like to share with me, or is this something I just need to experiment with?

Thanks!
Jerry
www.jerrygerber.com

I have an Esprit 100ed, 2600mm Pro camera on an iOptron GEM45 mount… I have 2 large dust ‘bunnies’ somewhere inside the optics.
After imaging I take Flats and Flat Darks for each filter and stack the Flat Darks in Pixinsight under the Bias Tab…
I have totally clean sub frames using this method…
Hope that helps
CS Olly

Thanks Olly. I hope the Esprit didn't come with the dust bunnies from the factory! I'm a fan of your gallery, I really love the image of the Soul Nebula you took with the Esprit 100, it's amazing and beautiful..

Jerry

Ah that’s most kind Jerry, I love the Esprit it’s such a great match to the 2600 sensor 👍🏻

With my qhy294m , only dark flats work and only if they are longer than 3s. Calibrating the light with bias or shorter than 3s flat/dark flat giving out result with terrible mottled background which is impossible to fix. This is well documented behaviour of this sensor.

In reading through this thread, it seems there is some level of misunderstanding what "flat darks" represent. Per my understanding and please someone correct me if I am wrong, "flat darks" are by definition darks. They are just darks take for the same length of time as each flat frame. For my 294mm and mc this is 6 seconds to resolve any banding. Thus, it should never matter what filter they are taken with. In all actuality, they should be taken with the lens cap/cover on and not attached to the OTA. With this in mind, they should be updated periodically as the sensor ages, every 3-6 months similar to any normal dark length category (180s, 240s, 300s etc.)

In contrast, flats needs to be taken every imaging session (especially for longer focal lengths where dust is more apparent). Flats are characterizing the OTA as it was as close to the last capture. This is where dust and vigenetting can be accounted for and subsequently calibrated out of the light subs. The time equivalent darks are used to calibrate the flats (ie baseline read noise, hot pixels, amp glow).

Flat Darks = characterize the sensor read out for a short time equivalent length as the flats

Flats = characterize the entire optical system at time of capture

Hi all,

Typically, I take both dark flats and bias and let Pixinsight sort out what to apply. I understand the discussion about using bias v dark flats (in that bias is already part of the dark flat) but does it hurt me to include bias in my batch pre-processing? For me, taking bias only takes a few seconds, but I'm wondering if I am inadvertently causing a double subtraction of bias value?

Arun H:
Jerry Gerber:
It appears to me that either bias or flat darks will work. I'll have to experiment. Nothing beats direct experience!

You can experiment - or you can use fundamentals.

The flat-dark that you take, which is a dark with the same exposure time as your flat, already contains the bias signal. So there really isn't any downside to calibrating with a flat-dark. The only requirement for proper calibration with a flat-dark is that the flats be the same exposure time as the flat-dark. And this is especially easy with a color camera, since you dont need to worry about the complexity of filters. Just decide what ADU number you want to target, set your panel to the brightness required to get a desired exposure time (usually greater than 3 seconds) and it is the same every single time. So I guess I don't see the benefit of going with a bias for a color camera, especially given the known issues with some of them.

I personally use the 2600 MC. I calibrate using flat-darks. I've never used a bias for any of the CMOS cameras I've had (ASI1600MM, 294MM, 2600 MC).

Thanks Arun! I can see from your gallery you know what you are doing, beautiful images!

No conflict between using fundamentals (and knowing what they are!) and experimenting. Both are essential to any kind of creativity...