M83

[rustigsmed]

Hi guys,

Here is my recent M83 the southern pinwheel galaxy. M83 was near the zenith so I thought i'd go for it and broke my own 3 minute sub rule and went for 5 mins. that resulted in fogging crazy gradients which increased the difficulty in processing, thus its an extremely black clipped picture to hide the gradients (as you can tell by the barely visible small galaxies next to m83). But the galaxy itself looks nice so I thought i'd post up here.

Big version below
https://www.flickr.com/photos/80336656@N07/17987972402/in/dateposted-public/lightbox/

Clear skies

Russ

[kosh]

Nice one Russell.
You managed to get more Red than I did in my most recent version.

Goran.

[rustigsmed]

Thanks Goran :)

[raymo]

The longer subs show more detail than my shorter ones do. I notice that
the whole image has a slight mauve/red tinge. Have you tried the gradient removal method that cometcatcher detailed in my recent post
of 5128?
raymo

[Robert9]

Luv it! Well done :thumbsup:
Robert

[rustigsmed]

Hi Raymo, yes the longer ones give more of the finer detail I think, but short subs can still give good results on m83 my previous effort was on my alt az goto dob (20 sec subs) which came out pretty well.

I did do that method it mostly worked although I was left with a donut around that I couldn't quite get it 100% uniform in this case. i might go back and have another crack but this is my second version of working on the processing which was a major improvement on my first version (i literally deleted that version off flickr today).




Cheers Robert!

[britgc]

That looks awesome Russ!

[vlazg]

Great pic Russ, lots of detail

[jsmoraes]

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.

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. :mad2:
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.

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.

[rustigsmed]

Cheers Bret glad you liked it!



Thanks George :thumbsup:



Hi Jorge,

Thanks for the comments and taking the time to go through your experimentation, unlucky the clouds rolled in when they did. We nearly have identical scope setups from memory :thumbsup:

The problem I have is that when I capture a sub (example the 5 minute sub) it looks good on the backyard eos and on my laptop but when I get it back to my real computer I have it evenly white over the entire image. think from sky glow (this is even with the CLS CCD). I haven't got a M83 sub to show at the moment but here is a 3 minute sub I took which looks like about as far as it should go https://www.flickr.com/photos/80336656@N07/16877388715/in/dateposted-public/ it is to the south which has less pollution too. I'll post up an M83 sub later tonight to show the 'whiteout' for comparison.

Good luck with your investigations :thumbsup: I need to stop being greedy on my sub length I think. (although recently I managed 30min subs with Oiii filter but that's a bit different).

Cheers

Russ

[jjz]

Great image and some interesting observations.

I wonder how your experiences tie into the Sensor Specifications seen here: http://www.sensorgen.info/

I am a complete newbie, but I have noticed better results with shorter subs. I am just slowly increasing the time to find the sweet spot for my setup.

JJZ

[rustigsmed]

Thanks Joe, yeah interesting stuff on the different sensors.

Here is a single sub as mentioned in my older post, almost looks alright but its just too much.
https://www.flickr.com/photos/80336656@N07/18457701826/in/dateposted-public/lightbox/