SharpCap Forums

I have been getting some very noisy images while livestacking, and thought perhaps using flats and darks may help. I tried it a couple of times and got poor results, probably because I didn't have the settings correct during capture of darks and flats. I understand that flats and darks must be captured in advance of livestacking then chosen to be applied during the livestacking process.

When capturing dark frames in advance, I chose "capture dark" in the capture menu. Then I used all the same settings used when running livestacking - the gain was set to about 400 and the exposure set to 5 minutes, with the telescope lens cover on. Is that the correct way to do it?

For flats, I used a light panel, set the exposure to be 50% (white curve) on the histogram, and set the gain at about 400. Is that correct? Note- the instructions on the "capture flat" screen said to set a low gain... this is different from other references I used that said to use the same gain used during capure. Which is correct?

Thanks,
John

Correction to my post - I set the exposure to 5 sec when capturing the dark frames (not 5 min).

Hi John,

your procedures sound correct for capturing darks and flats, but I'm not sure that they will help much in the case of having noisy images.... Flats and darks have their own specific roles to play correcting certain issues that you can get when imaging, but using them will in fact add *more* noise the image (some noise comes from the flats and darks).

To be more specific:

* Flats will help deal with brightness fall off towards the edges/corners of the image (vignetting) and also dark spots caused by dust on the sensor or on filter glass surfaces.

* Darks will help remove pattern noise in the image - this could be bright areas caused by 'amp glow' that are seen in dark frames or hot or warm pixels that show as bright in dark frames even in the absence of light.

Very noisy final images have a few possible cures

1) Take longer sub exposures up to the recommendation of the SharpCap smart histogram brain (very little gain going longer than the suggestion)

2) Longer total imaging time - 4x longer will halve the noise

3) Reduce the amount of light pollution in the background by using filters or moving to a darker site.

Of course, none of these are easy cures for the problem sadly

cheers,

Robin