SharpCap Forums

Hi Robin and all,

See attachment 1, zoomed to 100%, a five minute sub, showing a lot of noise and or hot pixels?

The 2nd attachment is the result of adding dark frames using the folder monitor camera. It appears to have removed the noise, but has completely darkened the image, no longer is M1 to be seen. Notice a reduction in the histogram. I made sure that the darks were taken at the same exposure, gain, and focus as the subs.

The third attachment is a zoom of 100% showing no noise. Interestingly, I reran using PI and it did not remove all the noise.

What can you recommend I do to improve this situation?

I look forward to your response.

Thank you.

Setup: 8” cpc EdgeHD w/ wedge, .7X reducer, asa183MC, OAG with PHD2

Hi,

firstly, when you subtract a dark frame, it removes the typical background level that each camera adds to the image data. There will still usually be some background left (from light pollution, etc), but the histogram is supposed to move a long way to the left when you activate dark subtraction.

However, from your screenshots it looks as though the histogram peak has been pushed all the way to the left - that is usually a sign that the 'dark' frame is too bright, possibly because it was taken at different settings to the light frame. In particular you should check that the exposure, gain and black level/offset/brightness settings are the same (the last one has different names on different brands of cameras).

As a check, you can look at your saved images in a FITS viewer and check that the average value of the light frames is higher than that of the dark frames. I suspect it may not be in your case due to settings being different.

cheers,

Robin