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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 15 Dec 2010 (Wednesday) 18:55
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"True" ISO

 
bsaber
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Dec 15, 2010 18:55 |  #1

I read on a thread on here a long while ago about the "true" or native ISO that cameras support. Not talking about ISO 100, 200, etc. but ISO 160, 320, etc. Can someone with more knowledge explain to me why that is? Why not have the native ISOs at 100, 200, etc?

And if the native ISOs are 160, 320, etc, does that mean that the dynamic range and noise are higher because they're being pushed or pulled in-camera?




  
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bsaber
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Dec 16, 2010 00:06 |  #2

I found this while searching online. Might be of interesting read to someone: http://shootintheshot.​joshsilfen.com …canon-hd-dslr-native-iso/ (external link)




  
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tfd888
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Dec 16, 2010 03:15 |  #3

bsaber wrote in post #11461002 (external link)
I found this while searching online. Might be of interesting read to someone: http://shootintheshot.​joshsilfen.com …canon-hd-dslr-native-iso/ (external link)

Good reading there! Thanks for the link :D


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tonylong
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Dec 16, 2010 03:37 |  #4

Well, from what I understand, for most Canon cameras, the "standard" ISOs, 100, 200, 400, 800, 1600, and then whatever the camera sets as standard, are ISO that are "electronically amplified" from "base", where light collected is optimized as much as possible. For Canon, ISO 100 is considered a base. so, ISO 200 amplifies an ISO 100 by a stop.

The +1/3 intermediate ISOs are amplified by software, whereas the +2/3 intermediate ISOs are reduced from the next-highest ISO. So, ISO 125 is actually an ISO 100 shot that has been boosted by software by 1/3 of a stop so may have the "proper exposure" but will be more vulnerable to noise in the shadows, whereas an ISO 160 shot will actually be an ISO 200 shot, amplified electronically, then reduced in software. It will have less shadow noise because you have actually brought down exposure, but will have less latitude in the highlights.

Then, the High and Low ISO follow a similar pattern -- Low ISOs will lower the exposure of the next "real" ISO up, so that ISO 50 allows a slower shutter speed then takes that overexposed shot and lowers the exposure in software by a stop. In the same way an "H" ISO will allow an underexposed shot and boost it by a stop.

In short, I'd say that if you are shooting jpeg, use what will give you the best results out-of-the-camera and let the camera do it's calculations, but if shooting Raw, you can match or beat those results if you understand the ideas involved.

I've heard that some Canon cameras have more "real" ISO range, as in the 1D series, but I haven't seen the evidence for that.


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focus.pocus
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Dec 16, 2010 03:47 |  #5

thanks for the link... very informative...


I know, right? I'm just sayin'...

  
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jra
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Dec 16, 2010 04:49 |  #6

tonylong wrote in post #11461618 (external link)
I've heard that some Canon cameras have more "real" ISO range, as in the 1D series, but I haven't seen the evidence for that.

I've also read that the 1D series cameras don't use a software push or pull but instead all of the ISO's actually reflect the amplification of the signal. I can't remember where I read it and I'm not exactly sure how reliable the source was. Even though it really doesn't make much difference in the "real world" of photography, it would be interesting to know :)




  
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Dec 16, 2010 05:13 |  #7

jra wrote in post #11461743 (external link)
I've also read that the 1D series cameras don't use a software push or pull but instead all of the ISO's actually reflect the amplification of the signal. I can't remember where I read it and I'm not exactly sure how reliable the source was. Even though it really doesn't make much difference in the "real world" of photography, it would be interesting to know :)

I first read this several years ago in a paper presented by Emil Martinec, a physicist at the University of Chicago, who impressed me as knowledgable:
http://theory.uchicago​.edu …oise/noise-p2.html#SNR-DR (external link)
It's a fascinating read and I fortunately bookmarked it. To quote from the section "Read Noise Vs. ISO":

"Higher end Canon models implement ISO gain via a two-stage amplification system; one amplifier for the "main" ISO's 100-200-400-800-1600 etc, and a second-stage amplification to implement the "intermediate" ISO's 125-250-500-1000 etc. and 160-320-640-1250 etc. ...... Lower end Canon models do not perform analog amplification for the intermediate ISO's, rather the intermediate ISO's are implemented by a multiplication of the raw data in software after quantization, and there is only a single stage amplification in hardware; strictly speaking, they do not have intermediate ISO amplification."


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stsva
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Dec 16, 2010 09:57 |  #8

tzalman wrote in post #11461776 (external link)
I first read this several years ago in a paper presented by Emil Martinec, a physicist at the University of Chicago, who impressed me as knowledgable:
http://theory.uchicago​.edu/~ejm/pix/20d/test​s/noise/noise-p2.html#SNR-DR (external link)
It's a fascinating read and I fortunately bookmarked it. To quote from the section "Read Noise Vs. ISO":

"Higher end Canon models implement ISO gain via a two-stage amplification system; one amplifier for the "main" ISO's 100-200-400-800-1600 etc, and a second-stage amplification to implement the "intermediate" ISO's 125-250-500-1000 etc. and 160-320-640-1250 etc. ...... Lower end Canon models do not perform analog amplification for the intermediate ISO's, rather the intermediate ISO's are implemented by a multiplication of the raw data in software after quantization, and there is only a single stage amplification in hardware; strictly speaking, they do not have intermediate ISO amplification."

That link was part of the epic thread that led to HAMSTTR. Good stuff! :)


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bsaber
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Dec 17, 2010 01:37 |  #9

Thanks for all the replies, good info here! :)




  
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tonylong
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Dec 17, 2010 02:32 |  #10

tzalman wrote in post #11461776 (external link)
I first read this several years ago in a paper presented by Emil Martinec, a physicist at the University of Chicago, who impressed me as knowledgable:
http://theory.uchicago​.edu …oise/noise-p2.html#SNR-DR (external link)
It's a fascinating read and I fortunately bookmarked it. To quote from the section "Read Noise Vs. ISO":

"Higher end Canon models implement ISO gain via a two-stage amplification system; one amplifier for the "main" ISO's 100-200-400-800-1600 etc, and a second-stage amplification to implement the "intermediate" ISO's 125-250-500-1000 etc. and 160-320-640-1250 etc. ...... Lower end Canon models do not perform analog amplification for the intermediate ISO's, rather the intermediate ISO's are implemented by a multiplication of the raw data in software after quantization, and there is only a single stage amplification in hardware; strictly speaking, they do not have intermediate ISO amplification."

Hey there, Elie:)!


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John ­ Sheehy
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Dec 21, 2010 14:11 |  #11

tonylong wrote in post #11461618 (external link)
I've heard that some Canon cameras have more "real" ISO range, as in the 1D series, but I haven't seen the evidence for that.

No one ever shows or tests the 1/3-stop ISOs for most cameras.




  
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John ­ Sheehy
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Dec 21, 2010 14:18 |  #12

jra wrote in post #11461743 (external link)
I've also read that the 1D series cameras don't use a software push or pull but instead all of the ISO's actually reflect the amplification of the signal. I can't remember where I read it and I'm not exactly sure how reliable the source was. Even though it really doesn't make much difference in the "real world" of photography, it would be interesting to know :)

I don't know about all, but at least one of the 1D cameras and the 5D original use analog gain for 1/3-stop ISOs, and extended ISOs as well, but do it after the noisy stages, so it is just empty magnification. The highlight headroom is the same for all, though. In the 5D original, 160, 320, and 640 are the bad guys, not 125, 250 and 500, like the 5D2 and the APS-c Canons.




  
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Dec 21, 2010 14:29 |  #13
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The only way to shoot true Native is to shoot Natives, or Indians, in the wild and if you do it naked thats Native Squared.


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nicksan
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Dec 21, 2010 15:12 |  #14

Hmm...I just dial in whatever ISO I need for the situation and shoot. But then again, I am simple minded that way...:lol:;)




  
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bsaber
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Dec 21, 2010 18:07 |  #15

EL_PIC wrote in post #11492238 (external link)
The only way to shoot true Native is to shoot Natives, or Indians, in the wild and if you do it naked thats Native Squared.

:lol:

nicksan wrote in post #11492449 (external link)
Hmm...I just dial in whatever ISO I need for the situation and shoot. But then again, I am simple minded that way...:lol:;)

Simple is good ;)




  
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"True" ISO
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