Dark frames questions

[Oberon510]

Hi,

I am using an ASI6200MC (Colour) camera for DSO work and I want to double check the setup of dark frames and their usage.

My images are all at full size (no ROI), same gain, brightness and exposure times as the dark frames and sometimes I won't use a light frame if there are no imperfections in the imaging train. I am averaging 10 frames for the darks setup - my current 600s dark based on 10 frames is 124mb.

My questions are:-

1) Would averaging more frames for the darks be better noise management?
2) Do I need to capture a similar light frame and apply it during image stacking or will it be OK just to use the dark?
3) When using a filter I just use the dark frames from no filter - is there any need to create a filtered dark frame?

Attached is an image and it's corresponding dark frame - captured using live stacking.

Thanks,
Ken

[Oberon510]

Item 2 should be:-

2) Do I need to capture a similar flats and apply it during image stacking or will it be OK just to use the dark?

Thanks,
Ken

[admin]

Hi Ken,

firstly for flat frames - they solve a different problem... If you see dust shadows on the image or darkened corners from vignetting then you should consider using flat frames. If your sensor is clean with no dust and your telescope is fully illuminating the corners/edges of the sensor so there is no vignetting then you do not need flat frames

Now, on the subject of dark frames - it's a difficult one to give a 'one size fits all' answer to. If you use a small number of dark frames (compared to the number of light frames) *and* the dark areas of your images are truly dark (either really dark skies or narrowband filters) then the remaining noise in the 'master dark' may have a noticeable effect on the noise of the final image. In those cases, taking more dark frames could help. On the other hand, if you have light polluted skies, so that the background isn't truly black due to the light pollution then the noise in the darker areas will be dominated by the shot noise from the light frame light pollution component, and a small number of darks won't make much impact.

Probably the best bet is to try with a significantly increased number of dark frames (say go from 10 to 40) and see if you see any difference. The nice thing is that you can take the dark frames at any time You don't have to take separate dark frames for different filters, since there isn't any light getting to the sensor for the dark frames anyway - at least there shouldn't be!

cheers,

Robin

[Oberon510]

Thanks Robin. I will give your suggestions a go.

Cheers,
Ken