Nick Cook
Pooh-Bah
Reged: 01/28/06
Posts: 1239
Loc: Somerset, England
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As I prepare to serioulsy launch myself into the world of imaging, I can't help but notice that many of you are using 1600 ISO with stunning results. These images seem to be turning conventional thinking on its head.
I would have expected much more noisy images at 1600. How come your images are so good? Until recently I would have thought 800 ISO was probably the best general setting, now I'm not so sure.
What's your secret?
Thanks,
Nick
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Meade 14" RCX + Astro Physics 0.75 Reducer (27TVPH)
Meade 5000 ED80 APO (Guider/widefield)+ WO 0.8 Reducer
William Optics Zenithstar 66 Petzal
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www.nick-cook.net
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Mike B.
Carpal Tunnel
Reged: 10/24/05
Posts: 2113
Loc: Louisiana
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The secret of using the 1600 ISO setting for imaging and getting a good picture is to stack enough subs to reduce the noise to acceptable levels. I try to get 35 to 45 subs for a relatively bright object and up to 60 or more sub-images for dimmer stuff.
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Clear skies!
Mike B.
My Astrophotos
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Andrew Welsh
Carpal Tunnel
Reged: 03/28/06
Posts: 2571
Loc: Rochester, NY
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Lots 'o subs. More exposures increases the signal to noise ratio, and thus you can 'bury' the noise in the signal. I prefer to shoot ISO 800 if I can due to increased dynamic range, especially in the summer.
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LX200 8" classic, f/10, Meade eq. wedge, .63x FF/FR
Canon 40D (LifePixel clear glass mod) and 5DMkII, unmodified
Canon EF 200/2L IS, 400/5.6L, 100/2.8 Macro, 50/1.4, 85/1.8, 35L, 24L, 17-40L and Peleng 8mm fisheye
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Pimped out with accessories and bling
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DaveD
professor emeritus
Reged: 03/03/06
Posts: 691
Loc: Santa Cruz, CA
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Another thing that is probably helping right now is that its winter (for most of us anyway) and the colder temperatures help keep the noise down. My last session the temperatures were around 60F and I noticed more noise in my individual subs.
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Dave
WO ZS 110, Celestron Classic C8,
Orion Skyview Deluxe 8, AT-66
Losmandy GM8
Canon 350D(modded), Minolta 5D, Celestron Neximage
Dave's Astrophoto Page
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Ptarmigan
Lagopus lagopus
Reged: 09/23/04
Posts: 3510
Loc: Arctic
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ISO 1600 also means less exposure time needed as compared to ISO 800 and less.
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s58y
Postmaster
Reged: 12/12/04
Posts: 6505
Loc: Eastern NY
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Question: Do you capture more with 60 2-minute subs at ISO 1600 than with 30 4-minute subs at ISO 800? (There might be more readout error with more subs, but does the reduced quantization error at ISO 1600 overcome this?)
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Hutech 500D/T1i, 550D/T2i, DMK21AU618, SBIG ST-402 autoguider
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Andrew Welsh
Carpal Tunnel
Reged: 03/28/06
Posts: 2571
Loc: Rochester, NY
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Quote:
Question: Do you capture more with 60 2-minute subs at ISO 1600 than with 30 4-minute subs at ISO 800? (There might be more readout error with more subs, but does the reduced quantization error at ISO 1600 overcome this?)
This was a classic question discussed a while ago.. I believe the result was there is an increase in overall noise / decrease in S/N ratio with the 60 x 120s stack, due to the increased number of subs. The lesson was it's better from a S/N perspective to take fewer subs for longer. And even if it's not, you at least have some gains in dynamic range. There are folks on the board who would have more knowledge on this... or read through that lengthy thread I posted- it's in there somewhere! (so glad the search function is working again BTW)
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LX200 8" classic, f/10, Meade eq. wedge, .63x FF/FR
Canon 40D (LifePixel clear glass mod) and 5DMkII, unmodified
Canon EF 200/2L IS, 400/5.6L, 100/2.8 Macro, 50/1.4, 85/1.8, 35L, 24L, 17-40L and Peleng 8mm fisheye
Orion Apex 102mm (4") Mak-Cass
Pimped out with accessories and bling
My DSLR Astrophotography Webpage and photo bucket with full equipment list
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Mike B.
Carpal Tunnel
Reged: 10/24/05
Posts: 2113
Loc: Louisiana
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At the beginning of this month, I did a test with two "equivalent" exposures - 1x300 @ ISO 1600 and 1x600 @ ISO 800. My conclusions were that a set of the longer, ISO 800 subs would probably produce a better image since there was a lot less noise. However, the ISO 1600 sub edged out the other with a little more image density. I think that means the ISO 1600 set of subs might go slightly deeper, but you would not be able to stretch it as hard with the added noise.
Here are the test images:
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Clear skies!
Mike B.
My Astrophotos
My Astrobin Page
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s58y
Postmaster
Reged: 12/12/04
Posts: 6505
Loc: Eastern NY
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In this test, you collected twice as many photons during the 10 minute exposure at ISO800 (and also spent twice as much time). Wouldn't a better test be two 5-minute ISO1600 exposures average-combined?
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Hutech 500D/T1i, 550D/T2i, DMK21AU618, SBIG ST-402 autoguider
SV80S, TV102iis, EdgeHD 800
Lenses: 800mm, 180mm, 135mm, 105mm, 85mm
AP900, Barndoor tracker
http://www.flickr.com/photos/s58y/
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Mike B.
Carpal Tunnel
Reged: 10/24/05
Posts: 2113
Loc: Louisiana
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Quote:
In this test, you collected twice as many photons during the 10 minute exposure at ISO800 (and also spent twice as much time). Wouldn't a better test be two 5-minute ISO1600 exposures average-combined?
What I'm testing here is noise/frame. It just means that with an equal number of sub-images at each ISO setting, the ISO 800 stack would have less noise, but it would have taken twice as long to get. However, I bet that for a dim object, you could stretch the result more and bring out fainter details than the ISO 1600 stack.
In my case, I am trying to find a solution to my problem of getting deeper than I currently can when shooting ISO 1600. I've tried 5 minutes @ ISO 1600 (max for my skies) with 40+ subs and just couldn't stretch it hard enough to bring out the faint nebulosity in a dim object that I know is there. The results are too noisy. I want to try the longer sub-image at lower ISO approach to see if I can go past what I've been able to make ISO 1600 achieve.
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Clear skies!
Mike B.
My Astrophotos
My Astrobin Page
My New Blog Page
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 14043
Loc: Rockford Illinois
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Nice comparison test...
With the noise @ 1600, I actually like the 800 better.
Did you happen to test down to 400 (would that be 20 minutes?)??
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Neo... (Jeff)
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10" LX200-GPS/SMT UHTC "Draco"
 Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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Mike B.
Carpal Tunnel
Reged: 10/24/05
Posts: 2113
Loc: Louisiana
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Quote:
Nice comparison test...
With the noise @ 1600, I actually like the 800 better.
Did you happen to test down to 400 (would that be 20 minutes?)??
Thanks!
I thought the ISO 800 image to be better, too. I didn't test at ISO 400. And yes, 20 minutes exposure is needed to even it out if I did.
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Clear skies!
Mike B.
My Astrophotos
My Astrobin Page
My New Blog Page
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 14043
Loc: Rockford Illinois
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Yeah, and I think you'd loose about half the red response with the ISO400 also.
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Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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Nick Cook
Pooh-Bah
Reged: 01/28/06
Posts: 1239
Loc: Somerset, England
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This is fascinating. It certainly sounds like 1600 ISO is a very viable option in certain situations. I guess it also depends on your sky situation and how long you can go with an exposure. This will probably have an influence on this decision as well.
Nick
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Meade 14" RCX + Astro Physics 0.75 Reducer (27TVPH)
Meade 5000 ED80 APO (Guider/widefield)+ WO 0.8 Reducer
William Optics Zenithstar 66 Petzal
SBig STL11000M + AO-L + 3" Pyxis Rotator + 3" PDF Focuser
Canon 20Da + IDAS Filter
Pulsar 9ft Dome
www.nick-cook.net
www.cavebear.co.uk
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Qkslvr
Pooh-Bah
Reged: 06/23/06
Posts: 1316
Loc: NE Ohio, US
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With digital imaging, there no difference in the number of photons that hit the sensor for any given period of time.
There is however a difference in how the photon count is measured depending on the ISO setting. At ISO 1600 the photons from dim objects are easier to measure, But the photons from bright objects are likely to saturate the sensor.
But neither the physical number of photons nor the photon conversion efficency changes.
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Mike
Onyx 80ED/N8/CG-5/40D
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