Any Need for Integrating Dark, Bias and Flat Frames into a Ha Imaging Stack Using a DSLR and DeepSky Stacker ??

Hi,

From context I deduce you are taking bias and flats after *every* session? This is kind of an overkill. Bias frames are pretty much the only kind of frames you can keep for almost as long as you have the camera. And if your optical train doesn't change, you only need to take flats once in a while to correct vignetting. I know flat frames are also useful for reducing the effect of dust motes but realistically speaking dust motes fall under three categories: easy ones on the telescope which you remove by cleaning with a suitable cloth, easy ones on the sensor which you remove with the embedded ultrasound cleaner and slightly more challenging ones on the sensor which you have to use a blower or a cleaning kit to get rid of. Either way, the best treatment of dust motes is to clean them (or ignore them if they are at the edges). A flat just won't do the same job.  Bottom line: create a master dark and a master flat that match your ISO settings, and you can reuse them for weeks, months or years (in the case of the bias).

Darks are a different matter because they have to do with two factors that are dynamic: exposure and sensor temperature.

In my experience darks are largely unnecessary with a reasonably modern DSLR when ambient temperature is below 15 degrees centigrade (this tends to keep the sensor cool enough for thermal noise to be pretty much a non factor), unless there is virtually no skyglow (skyglow tends to saturate your sensor more than any thermal or random pattern would) _and_ you are exposing for several minutes. I am afraid the last two factors are definitely at play when doing Ha: the sky is ultra dark because of your filter and you have to expose for at least five minutes because of your filter.   There are basically two things you want to get rid of with darks: one is several hot pixels which will inevitably pop up in a long exposure. Those you can easily get rid of by dithering, by creating a bad pixel map or even with software. The other is thermal noise manifesting most prominently as a glow around the edges. This is generally very low on DSLRs but I would be very surprised if nothing showed up in a 5 minute  exposure. It is quite prominent on my D7500 once you go above 4 minutes or so. This kind of noise needs darks in order to be eliminated or at least reduced, but is also the trickiest since the duration and sensor temperature must match your lights quite accurately (not 100% accurately but say within a couple degrees plus or minus, YMMV of course). If your darks are not good, they end up making more harm than good.

So I guess the only way to know for sure is to experiment. Simply try integrating without darks (and the various different methods me and Janco outlined to get rid of hot pixels). If you find that you like the result (or that at least it is better than what you are getting with darks), by all means go on without darks. Otherwise perhaps you should start thinking about purchasing a cooled camera with low amp glow for doing your Ha, and use the DSLR for more traditional wide band targets where it really excels at.

Cheers,
Dimitris

Some great ccds with low noise, will not need darks. Does not apply to you with a dslr.

Actually, CMOS sensors (which includes DSLR cameras) tend to have much lower read noise than CCD sensors because of fundamental differences in design which cause the CCD readout to take longer.

For example the cooled Atik 4120 EX has roughly twice the read noise of the uncooled ZWO 178MC, despite the 4120 being a very high quality camera that costs 4+ times as much as the somewhat low end 178MC.

The fact that CCD cameras have worse read noise than DSLRs doesn't mean much though, because both kinds of cameras have insignificant read noise compared to 10-15 years ago. And it doesn't mean anything about the need to take darks: darks are not for readout noise, that's what bias frames are for.