Streaked images help :(

[Starcrazzy]

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?

Thanx:thumbsup:

[irwjager]

Hi,

I bet you didn't dither between frames, did you? :D
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.

Hope this helps!

[rcheshire]

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.