Very good image. With many details. Despite of some clipping, you got show the star nursery of this galaxy. I
never did well those nurseries.
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my own 3 minute sub rule and went for 5 mins
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I am worried with this. Some texts say that 10 x 3 minutes is the same than 6 x 5 minutes. The difference will be in noise signal: read noise, thermal noise, sky noise , noise of noise and many others sources of noises.
All arguments are very consistent. And I agree with almost them.
But ... Always will have a "
but" or an "
however-nevertheless". With Canons (DSLRs) I see differences not told.
1) more time for subs will increase the skyglow, and some faint details will be lost.
2) more time for subs will increase the diameter of stars and so will reduce the visibility of resolution (separation between two points). Therefore some faint details will be lost.
3) more time for subs will saturate the color of stars in DSS, that will make all them as white in stacking result.
Today, just now, I was betrayed by clouds.
But, I did 3 photos. One, for focus check with 10 seconds ISO 3200. Other with 240 seconds ISO 400. And the last 180 seconds ISO 800.
Normally we will say that 180s/800ISO is better than 240s/400ISO. The 180s/800ISO should be similar to 360s/400ISO. But, I didn't see it.
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that resulted in fogging crazy gradients which increased the difficulty in processing
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With 180s/800ISO the stars have a diffuse brightness around that isn't Airy disk. It remembers a fog, ilumination of fog around a source of light. It seems a little "bad focus". With some distortions.
For me, this is refraction from hight humidity.
With 240s/400ISO the stars have a pefect round stars, with sharp border. No fog around and no distortion.
Therefore the "laws": take with hight ISO, take with long time exposure aren't real laws.
Despite of atmosphere, I perceive that with stock DSLRs (Canons) there is limitation for long exposition and using stacking in DSS there is limitation in total time of capture.
This night, I was just trying to decide: what better time of exposition and the better ISO for a specific area of sky ? The sky I was intenting to shot, the better option was 240s/400ISO.
Clouds killed my efforts !
There are 2 tests that I want to do for solve some questions:
1) 1 hour is worse than 3 hours ? Forget the noise, see only the quality of stars shapes and color.
2) 1 hour with low ISO is worse than 1 hour with high ISO ? Stars shape and color.
It is difficult because it must be at the same night, with the same object and without Moon or clouds strolling around
Note: I believe that with mono CCD cameras and filters it is quite different. You see that better images is with many and many hours of exposition (we can say days !).
But, I don't remember to see images
with stock color Canon (DSLRs) with the same long time of exposition.
