Second M31 of season

[sdbodin]

Repeated the 135mm Rokinon test on M31. This time at f2.0 vice f2.8, but only 30 minutes vice 60, so the image density should be the same?? given the 'law' of f stops, right? I guess that there are too many other variables that can affect the results as the f2.0 is way deeper. Sky conditions are one, first shot transparency rated as fair, new one as very good. First shot, M31 only half way up, second, near transit almost vertical. Post processing, I never remember from one day to the next what I did, so inherently different in stretch levels, curves, etc... All this is done by eye anyway, but the basic processing flow was the same.

New image at f2.0...

Old image at f2.8...

Details, 135mm f2 Rokinon telephoto lens coupled to ASI1600MC-cool OSC with IR cut filter; at f2.0, 15/2 min subs, at f2.8 60/1 min subs. Both gain 200, offset 50, temp -15C, no darks, flats, bias, raw only.

So that is the end of testing the Rokinon, all shot will be a f2.0 and 2 min exposures from now on... except when they are sometimes not.
Steve

[messier 111]

nice difference , thx .

[bobharmony]

Very nice improvement, whatever the reason!

Bob

[Ken_nneth]

Great image, as you said many different things influence the end result. I feel that processing is many times makes the biggest difference.
Thanks for sharing
Clear Skies
Kenneth

[Gmetric]

Well, that turned out really well; totally different, which in Japanese is “全然違う”. Love it

[jthommes]

Steve ,
On a direct comparison, the f/2.0 image is clearly better. I suspect the different post processing / stretching had a lot of impact. The two images should see the exact same processing for a fair comparison. Also, I am not convinced that it is a 2 to1 equivalence to run 60 subs at 1 minute to 15 subs at 2 minutes. The 1 minute subs could be running into reciprocity issues particularly at that high gain compared to the 2 minute subs. Probably a better comparison is to run 15 subs at 4 minutes f/2.8 compared to 15 subs at 2 minutes f/2.0.

I have to agree though that anyway you look at this, seems you are definitely better to run 15 subs at 2 minutes at f/2 compared to 60 subs at 1 minute at f/2.8. I'm just not sure it is valid to expect that the law of stops can be predictive with all these other variables being different or uncontrolled.

[TheButcher]

Excellent Steve!

[STEVE333]

Rather amazing difference Steve. The new one is a beauty with lots of detail in the dust lanes and you brought out the blue nebulosity in the lower left edge of the galaxy. Nice job Steve.

Steve

[Ylem]

Awesome Steve!!!