What's going on here?

[groberts]

I've been working on B22 recently and something funny is happening with the luminance subs.  From the outset they look overexposed i.e. bright white at the time of capture but after stacking + some judicious stretching the detail's there +OK.  Out of the camera (unprocessed) the L subs histogram is heavily skewed to the right but can be corrected as described.  However, last night I got no detail at all with the luminance subs i.e. just a bright white subs which will not stack but the  RGB subs look OK. 

I had a software meltdown (using APT) earlier in January but after reinstalling and sucessfully completing a narrowband image I moved on to B22 when the above Luminance problem occurred.  I'm imaging with a ZWO ASI1600MM camera at Unity (Gain 139, offset 21) and 600 sec luminance + 300 second RGB exposures - been using this for years and not seen this problem before  

Any thoughts about what could be going on here?

         

Edited February 1, 2022 by groberts

[geeklee]

3 hours ago, groberts said:

600 sec luminance

This seems high for Luminance with the 1600MM at unity gain.  Looking at your site, you are taking your Lum typically at 300s (I see some 60s Lum too on a few images) with Ha subs typically at 10min/600s.  It might not be as simple as this of course but wanted to rule out the obvious - I remember accidently taking a very long Lum sub in quite bright skies once and it came out grey and the histogram on the right.

3 hours ago, groberts said:

However, last night I got no detail at all with the luminance subs i.e. just a bright white subs which will not stack but the  RGB subs look OK. 

With this though, I'm not so sure it could happen without being close to the moon with the longer exposure 🤔

Edited February 1, 2022 by geeklee

[groberts]

Yes I do usually use shorter luminance but looking at a number of images of B22 on Astrobin, which being a dark nebula is on the dark side, and most of the better ones seem to use 600 secs or at least 300 secs.

Been playing around this evening even with 180 secs + other settings it's still happening, so not sure what's happening! 

Thanks for your thoughts.

Graham  

[geeklee]

32 minutes ago, groberts said:

Been playing around this evening even with 180 secs + other settings it's still happening, so not sure what's happening! 

Thanks for your thoughts.

Sorry about that Graham.  Did the software meltdown include reinstalling ZWO drivers (both native and ASCOM) or just getting Apt up and running again?  Nothing unusual when you connect the camera and set the gain (e.g. it sometimes resets)?  Very strange it's just the Lum - it kind of pulls you away from thinking it's camera/hardware related. 

Can you take a Red sub, it's OK, then immediately take a Lum sub and it's bright white, then go back to Red (for example) and it's OK again?

Do you have any other software you can try to take a Lum sub with - Sharpcap maybe (or another capture prog of course).

[groberts]

Thanks Lee, one of those 'astrophotography problems' I expect, i.e. it's staring me in the face but will take forever to sort!  

No I did not have to reinstall any drivers and at first all seemed fine, as after sorting things I completed imaging a narrowband image without (as far as can see as it's not been fully processed yet) any problems.  As I initially said, the RGB subs seem OK imaging B22 and it appears to be only the luminace. 

I've only ever used APT and don't use any other capture software for mono imaging but I'm suspicous of the gain / offset settings, that seem to work a bit diferent with APT v3.90 which I updated to after the crash from v 3.88 and have posted a query on the APT forum for Ivo = watch this space!

Graham   

[geeklee]

9 hours ago, groberts said:

i.e. it's staring me in the face but will take forever to sort!  

9 hours ago, groberts said:

posted a query on the APT forum for Ivo = watch this space!

Fingers crossed you get a resolution.  Do the Gain and Offset values in the FITS file header of a Lum sub match what you'd set?

9 hours ago, groberts said:

I've only ever used APT and don't use any other capture software for mono imaging

No problem, I only threw SharpCap out there in case you used it for Polar Alignment.  It'd be quick to connect the camera to this for a few minutes to test.

[groberts]

The Fits header is fine and reflects the correct setting - waiting to hear back from Ivo 🤞 

 

[groberts]

It's embarassing but it seems like it was just overexposed and I wasted +5 hours imaging time, but I still don't really get it?

Spent two days checking setup and, as far as I can see, all's fine.  So with clear skies went out again on Friday and tried exposures at 300s = better, 180s = much better and 120s OK but probably a bit higher works best.  I therefore imaged 4-hours luminance at 180s + preliminary process (to check) and it seems good.  Attached below are 600s L sub (others were worse) and 180s stack + stretch.  

Notwithstanding, I went back to the original 600s L subs and although 90% were saturated some are actually OK + just to repeat, I originally researched other's work on this object B22 and was pursuaded that being a dark nebula the most popular exposures used was 600s or higher made sense. The bottom line is (a) I'm still not sure what's going on but the camera etc seem OK (b) I will be continuing @ 180s and chalking it up to experience + unexplained!

Thanks for the thoughts. 

     

  

    

[scotty38]

1 hour ago, groberts said:

I originally researched other's work on this object B22 and was pursuaded that being a dark nebula the most popular exposures used was 600s or higher made sense.

Just a thought but the other images you found at 600s plus were they CCD cameras by any chance?

[groberts]

Some were, some weren't.

Edited February 6, 2022 by groberts