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I watched this video by Dr Robin Glover (author of SharpCap) explaining exposure time and gain.
After watching that and using the formula, I determined my ideal exposure time to be about 23 seconds... I had been shooting 180 seconds until now.
So, now I'm capturing 600+ images a night vs the 150 or so before, which is a HUGE processing challenge but the results were decent so I ran with it for a while... This past week offered me 2 decent nights and I decided to put this to the test. Night #1 I imaged the Elephant's Trunk all night at 30 sec exposures, giving me about 600 images. Night #2 was also spent on the same target but at 180 sec exposures. I stacked 91 of them. I tried to process them in StarTools equally but I was forced to use a stronger initial stretch with the 30 sec image to achieve acceptable results.
Below are both images processed almost identically.
30 sec:
180 sec:
It's Much easier to work with ~100 frames than the 600+ and I'm not really noticing any return for my investment in time...
Just food for thought... Thanks for looking!
Larry
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.
For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with an OTA mounted mini PC
Tele Vue Paracorr Type 2 coma corrector
Altair Hypercam 26C
Thanks for doing the experiment and posting the results, Larry. To my eye, the stack of 30 second images looks just a tad sharper, more contrasty, and more detailed. It could be the exposure length difference, it could be differences in the process, could be the slightly higher total exposure time... I like the shorter exposure length result better, but can understand the pain of having to process 6x the number of subs!
Thanks Bob.
I like the 30 sec stack better as well. I think the initial stretch and a touch more saturation made the difference.
Honestly, I expected more star bloat in the 180 sec image but guess gain 0 kept it down...
Larry
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.
For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with an OTA mounted mini PC
Tele Vue Paracorr Type 2 coma corrector
Altair Hypercam 26C
What would the 180 second stack turn out like with the additional initial stretch that the 30 second stack had?
That's the $64,000 question... I couldn't duplicate that exactly because the two datasets were different in their brightness.
I just sort of guessed on the development to get it as close as I could...
Larry
For visual:
10" Skywatcher collapsible goto dob, various EP's and a Celestron StarSense auto align.
For imaging:
Orion 8" astrograph 800mm @ F3.9
Eq6-R Pro controlled by APT via EQmod with an OTA mounted mini PC
Tele Vue Paracorr Type 2 coma corrector
Altair Hypercam 26C
I say throw them all together and see what the total conglomerate looks like. The short exposures should control saturation and the long ones should reduce noise. The two combined may produce something quite pleasant.
I have always been interested in the many-short vs the few-long exposure(s) problem and I really like the experiment you provided here - nice. I still haven't really come to grips with one vs the other. Although the 30sec result looks sharper and has more contrast unless the initial subs and post-processing were really comparable its hard to claim the shorter sub was the driving factor. I still find that unless you expose long enough to allow photons to register you get nothing regardless of the stretch (obvious, I know!). And the dynamic range suffers with very short exposures stretched to a high degree, and that will degrade your final result. As is the case with most of these concepts, the sky condition/object/equipment makes it an it-depends issue. If you really analyze the problem you will find that there is (probably) an ideal exposure for each object. Let's keep the experiments going. I have some more examples I'm working on which I'll post when complete.
Scopes Celestron EdgeHD-11; William Optics GT102; William Optics ZS61; Criterion Dynamax-8 SCT Mounts AP1100GTO mount w/APCCpro; iOptron iEQ30 Pro; Criterion Dynamax-8 SCT Lenses Hyperstar-III; Celestron 0.7x FR; WO Flat/Reducer 0.8x Guiding Celestron OAG w/ASI174mm mini; WO 50mm; Orion ST80 Cameras and Filters ZWO2600mm Pro w/Optolong 3nm NB and RGB; ZWOASI1600mm Pro (ZWO LRGB and Astrodon Ha-5nm, Oiii-3nm, Sii-5nm), QHY10, Canon 50D; ASI174mm mini; ASI462MC; ASI120MC Misc Moonlite focuser on Edge - Feather-Touch focuser on GT102; ZWO EAF on ZS61; ZWO 2" and 31mm FWs; Kendrick Dew System, Temp-est Fans Software NINA; PHD; APT; BYE; PI; APP; PSP; Registax; FireCapture; SharpCap
Blog at: SkyAndRockets
Larry 1969 wrote: ↑Sun Aug 08, 2021 1:24 am
Good day all!
I watched this video by Dr Robin Glover (author of SharpCap) explaining exposure time and gain.
After watching that and using the formula, I determined my ideal exposure time to be about 23 seconds... I had been shooting 180 seconds until now.
So, now I'm capturing 600+ images a night vs the 150 or so before, which is a HUGE processing challenge but the results were decent so I ran with it for a while... This past week offered me 2 decent nights and I decided to put this to the test. Night #1 I imaged the Elephant's Trunk all night at 30 sec exposures, giving me about 600 images. Night #2 was also spent on the same target but at 180 sec exposures. I stacked 91 of them. I tried to process them in StarTools equally but I was forced to use a stronger initial stretch with the 30 sec image to achieve acceptable results.
Below are both images processed almost identically.
30 sec:
180 sec:
It's Much easier to work with ~100 frames than the 600+ and I'm not really noticing any return for my investment in time...
Just food for thought... Thanks for looking!
Larry
Very interesting video clip. Cleared a lot to me. Especially the terms.
And your experiment shows nicely how things work in real life.
(BTW, nice pictures.)
- Juha
Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5
I don't suffer from insanity. I'm enjoying every minute of it.