Page 1 of 1
M31 in 35 minutes with Altair 183M
Posted: Mon Sep 17, 2018 2:52 pm
by turfpit
- _M31-35x60s-g100-bl20.jpg (433.31 KiB) Viewed 3336 times
Altair Lightwave 66ED, Planostar 0.8x flattener/reducer, Celestron AVX mount, Altair 183M camera.
SharpCap + FITS Liberator + Nebulosity + GIMP 2.10
Focus with Bahtinov mask, unguided.
35x60s, gain=100, black level=20
35 lights, 30 darks, 30 flat, 30 bias
Session terminated by cloud bands and mist, so I processed what I had. This was first session with the camera, ideally I wanted to acquire 100 light frames and experiment with longer exposure.
I noticed some dropped frames, I think I need to increase the USB slider next time.
Dave
Re: M31 in 35 minutes with Altair 183M
Posted: Mon Sep 17, 2018 2:57 pm
by turfpit
SharpCap Capture screen for above image..
- capture-screen.png (90.34 KiB) Viewed 3332 times
Re: M31 in 35 minutes with Altair 183M
Posted: Mon Sep 17, 2018 6:23 pm
by admin
Dave,
just to confirm, the lower screenshot shows a single unstretched sub? Nice example of how stacking and stretching brings out fantastic detail. What would be seen as a screenshot if you'd used the 'autostretch' button on the mini historgam I wonder?
cheers,
Robin
Re: M31 in 35 minutes with Altair 183M
Posted: Mon Sep 17, 2018 8:47 pm
by turfpit
Robin
Yes that is an in-progress capture of a single 60s frame - progress at botton right is 20/40.
I can load up one of the frames later, stretch it and post back. It does clearly show M31 when stretched, that is how I ensure I am 'on target'. Mini histogram stretch is very useful. I can also post up what the final stack looks like.
This where it is very disconcerting for beginners because I don't have anything visible - I trust the histogram shape and LHS offset.
Dave
Re: M31 in 35 minutes with Altair 183M
Posted: Tue Sep 18, 2018 1:41 am
by turfpit
Robin
One of the M31 frames loaded into SharpCap using the Test Camera 1 (Deep Sky). Display Histogram stretch applied to show object of interest, M31, at the centre. Without the stretch, the capture display looks like the image above.
Dave
- display-histogram-stretch-demo.JPG (138.08 KiB) Viewed 3311 times
Re: M31 in 35 minutes with Altair 183M
Posted: Tue Sep 18, 2018 6:05 am
by admin
Thanks Dave,
I'm actually rather pleased that the auto level stretch does a pretty good job on that sort of image
cheers,
Robin
Re: M31 in 35 minutes with Altair 183M
Posted: Tue Sep 18, 2018 7:21 am
by turfpit
Robin
Yes, that feature alone is worth the price of the software!
When setting up for the start of the capture, I turn the gain up to around 50%. That way, combined with the stretch, I can drop the exposure to much less than the the target (60s in this case). This allows minor positional adjustments with the hand controller, usually by being able to see a bright star and adjust using that. Adjustment with the controller at 60s would not really work.
I will capture this sequence as a set of screens next time I am imaging.
Dave