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FORUMS Photo Sharing & Visual Enjoyment Astronomy & Celestial 
Thread started 19 Jan 2012 (Thursday) 08:34
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Why the high ISO?

 
Toxic ­ Coolaid
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Jan 19, 2012 13:35 |  #16

here is a good page that tells you what times go with what magnification.

http://www.astropix.co​m/GADC/SAMPLE7/SAMPLE7​.HTM (external link)




  
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ramv
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Jan 19, 2012 18:12 |  #17

..doesn't that just up the noise so much more? Seems in my mind a lower ISO would work better.

Even if you had a perfect mount and perfectly dark skies, you want to keep the ISO relatively high (say around 1600 for modern canon cameras like T1i and later and even higher for 5d mark II/full frame cameras).

The reason is that ISO 1600 has the highest signal to noise for a given exposure length. I can now hear several of you already thinking "this makes no sense, ISO 100/200 has the best signal to noise". Please also note that ISO 100 exposures are also many times longer.

If you could stack 16 exposures of 1/16 duration at ISO 1600, it would be lower noise than a single exposure at ISO 100. That holds whether you are doing astrophotography or anything else.




  
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Toxic ­ Coolaid
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Jan 19, 2012 19:30 |  #18

with my 1000D I usually stick to 800, and like ramv says, I use 1600 on my T2i




  
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CatchingUp
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Jan 19, 2012 21:46 |  #19

Ok....so this evening, I mounted my 15mm on my 5Dii. Set the ISO at 3200 @ 2.8 and used my wireless trigger for a 40 second exposure. I tried other ISO settings but seemed to like this one the best. Cleaned it up just a touch and would like some input on the photo. Pretty impressed with the number of stars that appeared because I sure didn't see that many looking up with my naked eye. Also...what are the reddish clouds of sort I see here...?

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jwcdds
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Jan 20, 2012 02:20 |  #20

The clouds are likely due to light pollution reflecting off the clouds from street lights off in the distance.


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huangyu84
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Jan 20, 2012 08:03 |  #21

CatchingUp wrote in post #13731175 (external link)
I've been dabbling some with night/star shots. I live out in the country so I do have some advantage of no city lights. But from what I'm reading on here, seems you all suggest the higher ISO. Why is that?

If I'm shooting 20-30 second exposures...doesn't that just up the noise so much more? Seems in my mind a lower ISO would work better.

Also...I tried some shots of Jupiter last night...with a 300 2.8 + 1.4 extender on my 7D. I was tickled to see some of Jupiter's moons...and realize I have to go with a longer exposure to capture the moons...but even with 2-4 second exposures, it looked like the moons were 'moving'...motion blur. I had my set up mounted on a tripod and used a wireless remote trigger. Surely the blur is not from planet rotation?

High ISO or low ISO it really doesn't matter that much when you talking about collecting photos from deep sky object. ISO will not affect how much photos you are collecting per each shot. However, a higher ISO setting enables you to detach the histogram from its base read out noise with relatively short time (usually limited by our tracking ability) and according to other reports, the current generation Canon DSLR has the lowest read-out noise at ISO800 or 1600. If the histogram is not completely detached from its base, the read-out noise will mess up the stacking process.

On the contrary, if you are living in a light polluted sky like me, a low ISO setting is more practical. I regular shoot with with ISO400 even lower to 100 to preserve the dynamic range under my light polluted sky.

hope this helps.




  
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archer1960
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Jan 21, 2012 08:53 |  #22

600/fl works for full frame cameras. For crop sensors, you really need to drop down to 500/fl, or even 400/fl to be very conservative. As for ISO, I find that 1600 works best on my T1i. 3200 is just too much noise; at 1600, a few darks will pretty much eliminate the noise once the final result is stacked. If I'm shooting single shots, I generally limit myself to 800.


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CaptainTonus
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Jan 24, 2012 17:06 |  #23

Another thing to consider about shooting at a higher ISO, the stars will "pop" way more, and more of them will show up in the shot, as the camera will be more sensitive to light. I almost always shoot ISO 400 or sometimes even 800 when I'm out at night. Depends on how dark your sky is and how much of a max. aperture your lens has.


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CatchingUp
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Jan 24, 2012 18:14 |  #24

CaptainTonus wrote in post #13762053 (external link)
Another thing to consider about shooting at a higher ISO, the stars will "pop" way more, and more of them will show up in the shot, as the camera will be more sensitive to light. I almost always shoot ISO 400 or sometimes even 800 when I'm out at night. Depends on how dark your sky is and how much of a max. aperture your lens has.


Wow...400/800 is not what I would call 'high' ISO. From what I was reading on other post, some were suggesting cranking the ISO up to 3200/6400 which was what prompted this thread to begin with.


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archer1960
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Jan 24, 2012 18:16 |  #25

CatchingUp wrote in post #13762452 (external link)
Wow...400/800 is not what I would call 'high' ISO. From what I was reading on other post, some were suggesting cranking the ISO up to 3200/6400 which was what prompted this thread to begin with.

How high is "high" ISO is going to depend on your body. 6400 on a 1D4 is nothing, but my T1i won't even go that high with a "real" ISO setting.


Gripped 7D, gripped, full-spectrum modfied T1i (500D), SX50HS, A2E film body, Tamzooka (150-600), Tamron 90mm/2.8 VC (ver 2), Tamron 18-270 VC, Canon FD 100 f/4.0 macro, Canon 24-105 f/4L,Canon EF 200 f/2.8LII, Canon 85 f/1.8, Tamron Adaptall 2 90mmf/2.5 Macro, Tokina 11-16, Canon EX-430 flash, Vivitar DF-383 flash, Astro-Tech AT6RC and Celestron NexStar 102 GT telescopes, various other semi-crappy manual lenses and stuff.

  
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CaptainTonus
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Jan 24, 2012 18:18 |  #26

CatchingUp wrote in post #13762452 (external link)
Wow...400/800 is not what I would call 'high' ISO. From what I was reading on other post, some were suggesting cranking the ISO up to 3200/6400 which was what prompted this thread to begin with.

Yeah, well, for a long time I was rocking a Rebel XT, and then a 40D. Those kinds of ISO's are not a possibility on those cameras. Anything north of 800 was totally un-usable on the 40D. I haven't had a chance to play with the 5D2 yet, but the one time I did get to use it for long exposure night stuff, ISO 1600 just overexposed the crap out of the sky. Way too much light pollution where I was at. :confused:


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archer1960
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Jan 24, 2012 18:29 |  #27

CaptainTonus wrote in post #13762475 (external link)
Yeah, well, for a long time I was rocking a Rebel XT, and then a 40D. Those kinds of ISO's are not a possibility on those cameras. Anything north of 800 was totally un-usable on the 40D. I haven't had a chance to play with the 5D2 yet, but the one time I did get to use it for long exposure night stuff, ISO 1600 just overexposed the crap out of the sky. Way too much light pollution where I was at. :confused:

IOW, you can shorten your exposures quite a bit, thereby reducing the trailing as well...


Gripped 7D, gripped, full-spectrum modfied T1i (500D), SX50HS, A2E film body, Tamzooka (150-600), Tamron 90mm/2.8 VC (ver 2), Tamron 18-270 VC, Canon FD 100 f/4.0 macro, Canon 24-105 f/4L,Canon EF 200 f/2.8LII, Canon 85 f/1.8, Tamron Adaptall 2 90mmf/2.5 Macro, Tokina 11-16, Canon EX-430 flash, Vivitar DF-383 flash, Astro-Tech AT6RC and Celestron NexStar 102 GT telescopes, various other semi-crappy manual lenses and stuff.

  
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CaptainTonus
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Jan 24, 2012 19:29 |  #28

archer1960 wrote in post #13762544 (external link)
IOW, you can shorten your exposures quite a bit, thereby reducing the trailing as well...

I don't have any issues with star trails. I had issues with being overexposed. Yes, I am aware that I could have stopped-down or shortened exposure times to compensate for this, but it would have resulted in less stars showing up regardless.


5D Mk2 + BG-E6 | Canon EF 24-70 f/2.8L | Canon EF 70-210 f/3.5-4.5 USM | 580EX II | Manfrotto 3021N/3030/RC2 | B+W Filters

  
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Why the high ISO?
FORUMS Photo Sharing & Visual Enjoyment Astronomy & Celestial 
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