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T2i's Optimal ISO?


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#1 ryan knight

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Posted 17 April 2010 - 12:18 AM

Now knowing that the 5/7D's optimal ISO settings are the 160, 320, 640, 1250... etc. increments, what ISO setting is optimal on the T2i (whose sensitivities are the in-between noiser "electronic gain boosters" - 100, 200, 400, 800... etc.)?

Anybody have any thoughts?
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#2 kyle merryman

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Posted 26 April 2010 - 01:02 AM

good question i'm wondering the same thing, especially since i'm thinking of getting the T2i as well :blink:
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#3 Jason Hinkle (RIP)

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Posted 06 May 2010 - 11:41 PM

Now knowing that the 5/7D's optimal ISO settings are the 160, 320, 640, 1250... etc. increments, what ISO setting is optimal on the T2i (whose sensitivities are the in-between noiser "electronic gain boosters" - 100, 200, 400, 800... etc.)?


hey ryan, i was looking for that info on the 7D recently. the weird thing is that if you turn off the "in between" stops on the camera, you would think those would be the optimal settings. however on the 7D the "full" ISO stops are 100, 200, 400, 800, etc. In other words 160, 320, etc are in between settings. But, I've read the same things as you recommended to use them. it seems like the opposite of what you'd expect.

do you happen to remember where you found those settings listed?
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#4 Jason Hinkle (RIP)

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Posted 07 May 2010 - 12:28 AM

i found this post which is a little too much science for me, but the guy sounds like he knows what he's doing - http://www.cryptobol...Canon7D_ISO.htm The relevant parts or the article seem to be:

(with ISO 340) "The camera's firmware multiplies the pixel values gained with ISO 400 by 0.8; this "shrinks" the pixel values (and causes the "combing" in the histogram); thus the shot appears for the raw processing software as if it had been made with the lower ISO gain.", "The same is happening with ISO 160, 640, 1250, 2500 and 5000 - they are derived from ISO 200, 800, 1600, 3200 and 6400, respectively. One consequence of this way of ISO implementation is, that shots made with ISO 160, 320, 640, etc. appear less noisy than with ISO 200, 400, 800, etc. Some users believe this is a reason to use these ISO steps. The reason for the lower noise is the 1/3 stop higher exposure, not the ISO difference itself. One can always reduce the noise by increasing the exposure, with any ISO, but this may cause clipping. "

Then for a more unscientific study, this guy did some video tests:
(7D noise test
(t2i noise test)

according to the video the 160, 320, 640, etc have way less noise. but the scientific article says that is just because the exposure is artificially increased on those settings.

The t2i looks simpler - the lower the ISO the better.
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#5 Mei Lewis

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Posted 07 May 2010 - 07:23 AM

I think you should both be very careful using any of the resources you've linked to.

I assume you're interested in the camera for video (given the forum we're on) but a lot of the information available about ISO relates to stills. What is best for stills shot in RAW and what is best for video might be very different. Video is captured in a compressed, 8 bit form with locked-in color temperature, similar to jpeg stills. There's a lot less information in each frame than is in a still RAW image.

The link you posted Jason http://www.cryptobol...Canon7D_ISO.htm specifically says "The conclusions are relevant only for those, who are working with the raw data; the considerations are different for the "JPEG shooters", choosing a setting, which is ideal for raw data may cause the JPEG image to become too dark or too bright. "

The vimeo videos don't seem to say if they're about stills or video, I assume because they're moving it's video.
They've exaggerated the results though to make them visible and they're only looking at noise which is not independent of dynamic range (see below).



-----------
AFAIK in stills general it's the whole number non-expanded ISOs that are 'best' e.g. on the 5D2 that's 100, 200, 400, 800, 1600, 3200.

'Best' here is in terms of noise AND dynamic range. I believe some intermediate settings are less noisy but at the expense of dynamic range. As JPEG and video have less dynamic range to start with it may be that some of the intermediate ISOs are better there as the loss of dynamic range isn't apparent but there is less noise.
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#6 Mei Lewis

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Posted 07 May 2010 - 07:26 AM

Just noticed this, also from the first link, which explains what I just said another way:

"One consequence of this way of ISO implementation is, that shots made with ISO 160, 320, 640, etc. appear less noisy than with ISO 200, 400, 800, etc. Some users believe this is a reason to use these ISO steps.
The reason for the lower noise is the 1/3 stop higher exposure, not the ISO difference itself. One can always reduce the noise by increasing the exposure, with any ISO, but this may cause clipping.
"
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#7 Hal Smith

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Posted 08 May 2010 - 03:19 PM

Two different points of view edited from cml:

#1

"So yes, ISO160 has less noise than any other ISO setting BUT the dynamic
range is shifted (highlights clip earlier). If the test was to compare film
vs HDSLRs and we all clearly know that they suck in terms of resolution, the
key point for many people watching the video was to see how close in terms
of DR SLRs are compared to film. But if you started by throwing away 1/3 of
a stop in order to get cleaner shadows the results are going to be
misleading."

ISO 100 = ISO 100
ISO 125 = ISO 100 + digital push --> more noise
ISO 160 = ISO 200 - digital pull --> less noise, less dynamic range
ISO 200 = ISO 200
ISO 250 = ISO 200 + digital push --> more noise
ISO 320 = ISO 400 - digital pull --> less noise, less dynamic range
ISO 400 = ISO 400

Miguel de Olaso
Macgregor™ DP

#2

"I was the one the certified the Zacuto test, we tested the image the same manner as I would for any video camera, I used a hardware scope. The only exception was that when we evaluated the content from the DSLR's we had to playback the content via the camera from the previously captured content as the live video out from any of the cameras was not ever full HD signal."

"We tested both the 5D and the 7D cameras and played back the content via an aja hi-5 converter (HDMI to HDSDI ) allowing us to view the full 1080 HD signal on a Leader LV 5330 where we evaluated the content. Signal noise was examined and based on that decision that Bob Primes and I made we handled all of the cameras at their lowest ISO rating of 160 and used this number (on a suggestion from Canon's onsite rep) as the interval for all of our ISO ranges."

"So we did not have some secret sauce or something special to handle the files, we just treated the signal as we would any HD Video source, our only issue was getting a proper signal out of the cameras in the first place."

gary adcock
Studio37

<Sarcasm ON>

OH NO!

You mean I have to TEST in advance of shooting? Just like the people shooting film have done since the days when Men were Men and the Movies were Silent?

<Sarcasm OFF>
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#8 Mei Lewis

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Posted 08 May 2010 - 05:50 PM

"...we handled all of the cameras at their lowest ISO rating of 160 and used this number (on a suggestion from Canon's onsite rep) as the interval for all of our ISO ranges."

But 160 isn't the lowest ISO of either camera, no matter hw you cut it, so is anything else they said correct either?
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#9 Hal Smith

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Posted 08 May 2010 - 07:11 PM

"...we handled all of the cameras at their lowest ISO rating of 160 and used this number (on a suggestion from Canon's onsite rep) as the interval for all of our ISO ranges."

But 160 isn't the lowest ISO of either camera, no matter hw you cut it, so is anything else they said correct either?


Depending on one's interpretation of all the data; If the Canon Rep said 160 one might assume that slower ISO's are the result of reduced gain.

All this is getting sorted out by the pros using these cameras. Sooner or later someone will come up with the definitive native ISO for the sensor which will clear up a lot of these issues.
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#10 Mei Lewis

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Posted 09 May 2010 - 02:55 PM

You might be right about 160 being the lowest 'true' or 'native' ISO.

I don't share your optimism about it all being sorted out though! It never really has been for any previous camera. The best I've seen is people shooting complicated tests and analysing the results with programs like DCRAW, and the results there are inconclusive, depend on the situation, or contradict other tests.

From everything I've read and tried, on the 5D2, I avoid ISO50 as it's a pull of ISO100 and loses highlight details. I pretty much never shoot over ISO6400 because the two higher settings are just too noisey. Between 100 and 6400 I just use the lowest ISO I can get away with.

I think the amount of noise plotted against ISO _is_ non-linear, and there may even be some inversions, but in practice it probably affects dynamic range too and it's too complicated to be bothered with for very small gains. I'd prefer to concentrate on getting the right photo than on slight noise level benefits.

E.g. it _might_ be that ISO6400 is just ISO3200 pushed a stop in camera, and in that case it would probably be better for technical image quality to shoot at ISO3200 and push it myself in RAW conversion. BUT if I did that the image on the camera's screen would look a stop underexposed and I'd have to meter differently for just that one ISO, so I couldn't make proper artistic judgements about the photo or show it to people on the camera.





BTW I'm a pro using a 5D2 ;-) Despite all the problems, I love it.
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