My first live stacks.

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AndyBooth
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My first live stacks.

Post by AndyBooth » Thu Mar 21, 2019 2:20 pm

Despite high cloud and a full moon, due to Robin’s inspiring talk and the images posted here, I tried my first Live Stacking session with Sharpcap, and my very modest CMOS camera.

As a startegy, I intend using my Altair GPCAM2 AR0130 mono for luminance, maybe through a light pollution filter, and then later, RGB through my Altair GPCAM3 224C,as they are same pixel and chip size. then combine to make LRGB.

So here are my mono M81 and M82 test shots. Only 60 frames in each stack, 80secs at gain 200, through an Altair RC8 operating at F4. Dark and flat used, but dark was not an ideal match.
Guided with PHD2 using 50mm finder and the GPcam3, on an EQ6.
A little post processing in Startools.

This is really promising! Obviously a lot of noise, I would want at least a couple of hundred frames based on this test.
Really easy to set up and capture too, great to see the image build on screen,
Cant believe the detail with cloud and full moon, and using effectively a guide or planetary camera.

C682D24C-B728-4C02-B738-B09553C1BDB7.jpeg
C682D24C-B728-4C02-B738-B09553C1BDB7.jpeg (139.39 KiB) Viewed 431 times
0B288018-C18C-4608-B54D-B18A06DE8308.jpeg
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oopfan
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Re: My first live stacks.

Post by oopfan » Thu Mar 21, 2019 3:24 pm

Hi Andy,

Great shots!

You said: "Only 60 frames in each stack, 80secs at gain 200, through an Altair RC8 operating at F4."
So exposure was 80secs or was exposure 80/60 = 1.33secs ?

Thanks,
Brian

AndyBooth
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Joined: Thu Mar 01, 2018 6:55 pm

Re: My first live stacks.

Post by AndyBooth » Thu Mar 21, 2019 3:42 pm

Thanks Brian!
Yes i can see its a little unclear, each frame was 80 secs long, and i took and stacked 60 frames. All at 200 gain and black point at 24.
To look at the sky was milky with only the brightest of the plough stars visible.

:D

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oopfan
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Re: My first live stacks.

Post by oopfan » Thu Mar 21, 2019 3:53 pm

Perfect!

How did you decide on 80sec exposure?

AndyBooth
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Re: My first live stacks.

Post by AndyBooth » Thu Mar 21, 2019 4:08 pm

used the brain on the histogram after doing sensor analysis.

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oopfan
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Re: My first live stacks.

Post by oopfan » Thu Mar 21, 2019 4:21 pm

Wow, you must have some very dark skies. I'm at Bortle 5. The Brain has never recommended exposures more than 15 seconds at Gain 200 and that's with no Moon! I don't use the Brain anymore. 30-second exposures consistently work very well for me.

For comparison here is a shot I took of NGC 4565 in LRGB:

William Optics 71mm f/5.9
Altair 290M camera (uncooled)

Gain 200 (1.74 e-/ADU, FWD: 7100e-, Read Noise: 1.55e-)
Luminance: 72x 25s
Red: 30x 30s
Green: 30x 30s
Blue: 25x 36s
Total integration time: 74 minutes
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NGC-4565_2019-02-10_LRGB_74m.jpg
NGC-4565_2019-02-10_LRGB_74m.jpg (155.56 KiB) Viewed 423 times

AndyBooth
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Re: My first live stacks.

Post by AndyBooth » Thu Mar 21, 2019 5:53 pm

Great shot, more inspiring stuff for me.
That is interesting, I am more like bortle 6 normally, but last night was even worse than that.
I did not use the the brain to measure the background however, I plugged in an electron value for sky background ahead of time
For the sky brightness. i normally get about 5 e/sec skyglow on that camera, with Bortle 6 @f4, and also aim for 4 or 5%
acceptable noise in the calculation.
Read noise on that camera at 200 gain is about 5e /sec, quite high.
To be honest I should have measured the sky background, but was rushed to get something :D
Theres a lot to learn. I also have a QHY10 CCD.

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oopfan
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Re: My first live stacks.

Post by oopfan » Thu Mar 21, 2019 7:48 pm

Very interesting.

So you have discovered what we in the "resistance" have known for quite some time: "burning in" sky glow is not a bad thing in fact it is beneficial for increasing the signal-to-noise ratio of faint nebulosity. The downside is that the brightest stars in your field will begin to saturate. So there is a balance you need to discover between acquiring low-noise sub-frames versus your tolerance for what I call "fat stars". With my telescope and camera I like to image targets that have stars no brighter than 10th magnitude. if I can crop out the bright stars afterwards then great.

Here is a good comparison:

A year ago I tried imaging M101. The Brain recommended an exposure of 9.4 seconds. I captured a total of 368 sub-frames in luminance for a total integration time of 58 minutes. The final stack was incredibly difficult to process since the galaxy was recorded just above the sky glow.

Last week I tried M101 again. This time I didn't use the Brain. I used my experience to tell me that a 25 second exposure was best. I captured a total of 47 sub-frames in luminance for a total integration time of 20 minutes. The final stack was a pleasure to process because the longer exposure gave the galaxy more time on the sensor to separate itself from the sky glow.

The image is noisy looking but that is because it is only 20 minutes of data. If it had been 58 minutes then it would blow your socks off.

Brian
Attachments
M101_368x9400ms Lights Darks Bias Flats Kappa FL.jpg
M101_368x9400ms Lights Darks Bias Flats Kappa FL.jpg (54.57 KiB) Viewed 412 times
M101 Lum 47x25s.jpg
M101 Lum 47x25s.jpg (364.62 KiB) Viewed 412 times

AndyBooth
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Re: My first live stacks.

Post by AndyBooth » Thu Mar 21, 2019 7:59 pm

Wow,
Now that IS interesting.
A great result! :shock:
That is my next target on the list.
What do you do about darks, have a pre made library, or go throught the pain each session?
Your read noise is also a big advantage at <2 e. i need to swamp my 5+ e.
Last edited by AndyBooth on Thu Mar 21, 2019 8:08 pm, edited 1 time in total.

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turfpit
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Re: My first live stacks.

Post by turfpit » Thu Mar 21, 2019 8:01 pm

Good effort there Andy particularly with cloud and full moon.

Don't underestimate what can be achieved with guide cams https://www.astrobin.com/359026/?nc=user. Looking forward to seeing what you capture with the QHY10.

Dave

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