M83

[kinetic (Steve)]

Pete,

I will PM my processing routine.
It might not work, I'm no expert, but you may want to give it a try?

Steve

[AlexN]

I dont know for sure, but I think that you're a long way from clipping any real data.. cant hurt to try I suppose... I'd be taking a few images that bring the main bunch of the histogram out a bit from the black point, and take a few shorter subs to mask the stars back in should they clip out badly ?

[peter_4059 (Peter)]

So are you keeping the histogram below 65k while imaging or setting the exposure time and then taking multiple times and masking to avoid clipping?

[Peter Ward]

Originally Posted by kinetic

............
Secondly, and at the risk of hijacking the thread, I think Peter Ward's
comments are a bit harsh....

You are entitled to that opinion. I don't comment often , but am definitely *not PC* (and make no apologies for that) and simply call it as I see it.

I had hoped to spur Pete on to try *much* longer subs for a truly great result.

Originally Posted by kinetic

that the lowly DSI Pro II
is still 16bit, so capable of 65,000 shades of grey.

No it's not... either lowly or 16 bit. A 16 bit D/A does not a mean a 16 bit image. The fact is: many CCD images are simply not 16 bit despite their D/A resolution...which includes many CCD's in the SBIG/FLI/Apogee range.

IMHO the image looks flat. Beautifully resolved (and hence really worth further effort) but flat just the same. Longer subs will bring out the really faint stuff....not seen thus far (ie low DR) ...but easily obtainable given the excellent result thus far.

[renormalised (Carl)]

I was going to suggest something similar myself....to get all the good bits it would pay to go longer on the subs. Just as long as his tracking and alignment are right.

[peter_4059 (Peter)]

Did a complete reprocess from scratch. Still a bit of noise. I think there is another close double at 2:30 in this image.

[jase (Jason)]

Spectacular work Peter. Keep them coming.

[peter_4059 (Peter)]

Thanks for the comments and advise Steve, Alex, Peter, Carl and Jase. Still trying to understand the merits of fewer long exposures or many short ones and how to manage clipping with longer exposures but will give some 5 min subs a try next time.

Peter.

[AlexN]

Some stars might saturate. but thats not that much of a big deal, although when they saturate they may bloat a little, costing you some of that magnificent resolution... However the longer your exposure, the more faint details you'll get... 100x1min images does not create an image as detailed as 10x10minute images... 10x10min will get more of the outer arms, a lot more dynamic range in your image, and a lot more background galaxies/stars etc.. 100x1min images may be smoother noise wise, because there is 100 subs to smooth it out... You may need to run some shorter subs to control the core of the galaxy though, as M83 is fairly bright in the central region..

Cant wait to see some 5 min subs!

Alex.