NGC 253 - Sculptor Galaxy

[mswhin63]

Hi All,

Finally getting the opportunity to image now, Managed quite a while concentrating on a single galaxy with a total 4 hours of shooting.

I have only process the 20 x 6 minute exposure @ 800 ISO. Result below. There are no flats or darks on this capture I may take a series of them tonight.

There are very few galaxies I can image due to 480mm focal length. Now that my shoulder is fully healed I will be considering larger focal length although first I will continue to shoot a few more larger objects for the 80mm F5.

Cheers

[Larryp]

Nice, Malcolm!

[Ross G]

Nice galaxy photo Malcolm.

Detailed and sharp.

Ross.

[mswhin63]

Thx Laurie and Ross.

I am though having difficulty with DSS with some Darks and Flats I took last night. The final image is horrible. It seems to be the darks that are causing the problem but have no idea why at this stage.

The Flats work well though and have a smoother over all image but still a bit noisy. The first image above I used Neat Image software to play with noise but needs improvement.

[PRejto]

I thought I might make a comment re darks. I've been having excellent results using CCDStack (I think there is a free 30 day trial!). Anyway, the technique I've been auditioning, which I'm sure is generally known by many, but was kind of new to me, was again mentioned by Adam Block in the CCDStack tutorial. Namely take 8-10 very long exposure darks.....I took 10 at 30 minutes (great for those cloudy nights), and take a very large number of bias frames at the same time. CCDStack does a great job with reduction by scaling the long darks to whatever exposure you take. I've found it unnecessary to take short darks to match short sub exposures and so far have been very happy with the results. You can even reduce a whole series of subs done to different exposure lengths at the same time. The program does darks, bias and flats all at the same time very quickly. I found the setup to be very easy.

[mswhin63]

I think the problem is that I use dithering as a method of noise reduction. The dark are not dithered so it think the reference is the same as far as noise. I a not 100% sure on this one but when the weather clears a bit more I will have a go without dithering.

Flats combined below

[PRejto]

Well, this may be a case of the blind leading the blind, but I think dithering and darks work to eliminate entirely different sorts of noise. You need good darks regardless, dithering or not, and there isn't any way to dither a dark anyway. What dithering can do is eliminate hot pixels which darks mostly cannot eliminate. Maybe this is too simplified but I think darks can mostly eliminate linear noise inherent in the CCD, and dithering can eliminate non-linear noise. I fail to see how a dark reduction could possibly make a frame worse if done properly. I wouldn't stop dithering!