Hi All.
I took this shot a couple of nights ago. Its 1hr 56 mins stacked in DSS.
Iso was 1600, 4 min subs. I normally only use ISO 800.
Im pretty happy with the shot although there is obvious diagonal streaking which is worst around Alnitak.
Any ideas why this has occurred?
I bet you didn't dither between frames, did you?
It's pattern noise that hasn't been spread/randomized across your frame.
Between exposures, try spiraling out from your initial position for best results.
That will fix it. Dithering works very well with DSLR's if you spread your images by 10 - 15 pixels. Makes a big difference to SNR as well. Improves image flatness and masks artifacts, such as hot and cold pixels and cosmic ray artifacts. Dithering also spreads your image over a greater selection of pixels, which is an advantage, given the varying health of individual pixels, you get more even sampling.
