SharpCap Forums

Hi Dave,

Last week I got two nights in a row of good seeing, now we are back into the "soup". I've been making a lot of software changes to my RA motor drive so I spent too much time on that and not enough time what I set out to do -- but I did get in 15 subs of NGC 7337 at 2 minutes each.

At the last minute I changed the game plan and decided on Brightness (i.e. "offset") of 2 instead of 3. (I should have gone with 3!) Well it was a dramatic improvement over Brightness of 0 that I used last month when imaging NGC 188. If you recall, Brightness of 0 (with Gain of 25) produced a thick green cast when I tried to push-process it to show stars at the limiting magnitude. Thanks to you I now know that this is caused by the light curve slamming up against the LHS of the histogram.

With Brightness of 2 I see that the histogram is shifted right with a tiny gap in between. When I push it hard I get a tinge of green around the stars, and on one corner of the image I get a little bit of green "space glow". All in all this is a major improvement. The next opportunity I get to image I will set Brightness to 3.

Sorry that I haven't forked off a new topic. I know how to do it -- I am just at a loss on how to begin it without people scratching their headings thinking "Where did this come from?"

Brian

Dave,

Last night I captured an hour of NGC 891 using Brightness of 3 and Gain of 25. Very nice results! Unfortunately I ran into guiding issues after an hour into the session and had to stop. I could have gone another 1.5 hours before morning twilight became an issue. I want to go for 2 hours total integration time. That should cancel the noise and bring out the detail in the dust lane of the galaxy. I'll post the image then.

So if you are interested in a middle-of-the-road setting for Gain 25 using the ASI120MC then I would recommend Brightness of 3. Don't go lower but you could experiment higher but at the possible risk of clipping stars at the RHS of the histogram.

By the way, with a 2 minute sub I was not able to see the galaxy in SharpCap or FITS Liberator. It was only after stacking that the galaxy revealed itself. That was with a 70mm/400mm $80 refractor.

Brian

Brian

Look forward to seeing NGC891. I will be experimenting with lower gains for DSOs when the weather permits.

I am still amazed by the power of stacking to reveal an object that cannot be seen visually in the scope.

Dave