Too Much Gain?

[JonCarleton]

I finally had a few clear evenings and got 100 moon shots that I was able to stack using Siril with very reasonable results.  Things worked "as advertised."  This more or less gives me a bit of faith in my ability to stack properly with Siril procedure-wise.  However, when I tried a similar procedure with 100 subs of the Great Orion Nebula, I am back to making things worse by stacking.  Since then, I have watched a number of stacking/astro videos and think perhaps I found a problem:

When I look at the moon, I crank the gain and exposure down to almost the lowest setting.  It is all I can do to get it low enough to avoid over-exposure.  When I try the M42, I focus on the stars, then crank the exposure and gain significantly higher until I can see a pretty good image with full color in the nebula on the computer.  Clearly, the main stars are over-exposed.  

In most of the videos I have watched, the sub images are not nearly as exposed or as high gain.  In fact, most of them don't even show much visible nebula until stretching the photo in post-processing.  

Next try, I'll try lower gain/exposure for the darker, deep sky images.  Am I on the right track?

[The-MathMog]

I would try that yes, as you can definitely end up overexposing some targets. Especially bright ones like the Orion Nebula.

What camera did you use, how long was the exposures, how high gain etc?

Even though M42 is quite bright, it is actually a hard target to expose right, without blending several exposure ranges, as it has a veeery bright cores, but faint flimsy parts.

The best results I've gotten, has been combining short exposures of 10-30 seconds with long 2-4 minute ones, or even adding even longer HA ones.

If you got a picture you could share, that would help too. But experimenting is always a good idea.

[JonCarleton]

Alas, I am an avid disk cleaner and no traces of my failures survive for long.  I am using a SVBony305, and used a 30 second exposure with about 60% gain.  By contrast, I use 1ms with 0% gain for moon shots.  This is the moon shot I stacked, though a bit overzealous in the GIMP post-processing.

I might get another shot at the nebula tonight and will post the results.

 

 

 

Edited April 5, 2020 by JonCarleton

[The-MathMog]

27 minutes ago, JonCarleton said:

Alas, I am an avid disk cleaner and no traces of my failures survive for long.  I am using a SVBony305, and used a 30 second exposure with about 60% gain.  By contrast, I use 1ms with 0% gain for moon shots.  This is the moon shot I stacked, though a bit overzealous in the GIMP post-processing.

I might get another shot at the nebula tonight and will post the results.

Nice image btw

Depending on the camera, as I am not familiar with it, it could definitely be a possibility that, that is too long an exposure / gain. As long as you are capturing files in a raw format, with the highest bit possible, you almost always pull out a lot more data, than is evident at the beginning. If you've overexposed, you can't really recover those areas.

Here is an example of what an image looks like for me, straight out of DeepSkyStacker - and then what a quick stretch in photoshop reveals

Edited April 5, 2020 by The-MathMog

[JonCarleton]

I found an image in the trash.  This is an example of an unstretched sub from an earlier session.  Still struggling with focus issues at the time.

[JonCarleton]

Yeah...I like your image.  I hope that =someday= I can get results like that.

 

[The-MathMog]

2 hours ago, JonCarleton said:

I found an image in the trash.  This is an example of an unstretched sub from an earlier session.  Still struggling with focus issues at the time.

That image doesn't seem all too bad. If you had a lot of those, stacked properly, I'd think that would yield good results.

Have you tried stacking with DSS?

And cheers - all trials and errors the last few years
 

[JonCarleton]

No.  I am of the UNIX religion.  I have evolved ever so slightly to Linux in recent years, but, "I don't do Windows."  I have tried RegiStax6 in Wine (Windoze emulator), but it is a bit buggy in that configuration and smells funny.  I do believe I have tried every Linux-capable stacking program there is, and my results among all of them seem similar.

I use the same process exactly with moon shots stacking and nebula stacking and the moon comes out OK, but the nebula looks awful.  As I said, the one I posted is one sub of 100, taken as FITS images (as were the moon subs).  I converted it to JPEG for posting in GIMP..

[Endolf]

Another Linux user here, have you tried astro pixel processor? seems to turn my subs in to something to be not too embarrassed by

[JonCarleton]

23 hours ago, Endolf said:

Another Linux user here, have you tried astro pixel processor? seems to turn my subs in to something to be not too embarrassed by

I may have tried it in my run of trying everything I could find, but it doesn't ring a bell.  I'll take a look at it.  Always willing to try recommendations from another Linux user.