"Native" ISO speeds for sensors?

nadtz wrote in post #5753658
In this case you are kind of wrong! A couple of pretty scientific tests were done by some dpreview and other forum users, noise characteristics in the 'tween ISO ranges could be higher than the next base ISO hop... The forum post above shows canon got it better tamed for the 40d, but the 30d wasn't quite so pretty.

http://www.adidap.com …non-eos-30d-iso-vs-noise/

Yes, I've saw that chart ages ago and I'm still not convinced. All the other noise vs ISO charts I've seen show otherwise. Just take a look at any of the "official" camera reviews that are out there, even in dpreview.com.

nadtz wrote in post #5753658
In this case you are kind of wrong! A couple of pretty scientific tests were done by some dpreview and other forum users, noise characteristics in the 'tween ISO ranges could be higher than the next base ISO hop... The forum post above shows canon got it better tamed for the 40d, but the 30d wasn't quite so pretty.

http://www.adidap.com …non-eos-30d-iso-vs-noise/

i'de help if people knew how to read graphs properly. canon between ISOs work like this: first 1/3rd stop higher is that stop+ software boost up 1/3rd stop. second third stop is +1 stop software boost down 1/3rd stop. hence a third stop lower will be lower noise than that stop. between isos are actually like iso 3200 and iso 50 (6400 and 50 on mkiii), they don't exist, rather they are just software changes in camera to an actual iso. what OP was talking about was standard ISOs, which are 100-1600 on all canon cameras except the 1d (200-1250, might be 1600 but can't remember) and 1dmkiii (100-3200), and 200-1600 on most nikons (a few max out at 1250)

So if I understand, using the "in between" ISO settings will cause you to lose a small amount of dynamic range (1/3rd or 2/3rds of a stop), while perhaps getting better noise control, correct?

gjl711 wrote in post #5751759
Actually I believe that the native ISOs are 100, 200, 400, 800, and 1600. ISO 133 is ISO pushed 1/3 stop, ISO 166 is ISO 200 backed off 1/3 stop and so forth. There is a good thread discussing this though I can’t find it right now.

From my understanding, Double negative has it right - there is but one "native" ISO value - in most cameras, the lowest ISO that can be selected. One exception is the 1D series, where ISO 50 can be selected.

A sensor will perform best at the native ISO - any variation from that will have measurable degradation - maybe not visible degredation, but measurable, none the less.

golfecho wrote in post #5751629
higher ISOs will produce more grain.

Higher ISOs will produce more grain only if aperture/shutter vary in the same ratio so that final RAW exposure remains the same.

But at a given aperture/shutter, you get less noise the higher the ISO, and more dynamic range (as long as you don't blow the highlights).

That is why you don't have to be afraid of pushing ISO under low light conditions, when you cannot get a good exposure at maximum aperture and slowest shutter. In those conditions, more ISO will reduce noise and enhance captured dynamic range.

ISO100 and ISO1600 samples taken at the same aperture/shutter, with exposure corrected in postprocessing:

I hope i neve have to push ISO 100 in post that much to get a correct exposure - it's ugly!

I wonder if the native ISO for 450D & 40D is 200. I base this purely on the fact that if you turn on extended dynamic range on these cameras they wont let you use ISO 100. the ISO range starts from 200.

If 100 is the native ISO, why does 200 give more (albeit marginal) dynamic range?

Something else that just occured to me..

All ISO's above the base/native ISO are made possible by boosting the gain on the sensor right?

So ISO 400, 800, 1600 (maybe 200 depending on whether 100 is the base or not) are all 'fake' iso's made possible by boosting the gain of the sensor. If what i read above is correct, to get the 1/3 stop ISO's (the latter of the two 1/3 stop) why the need to boost above it and then pull it back again?

For example say you choose ISO 640, why does the camera boost to 800 and then pull it back? As they're all fake iso's and just variable strength of signal boost, why not just boost the gain enough to reach 640? Pushing it to 800 and then pulling it back makes no sense at all to me.

If that is indeed the case then i'm sure there must be a valid and no doubt scientific reason for it that I wont understand!

FlexiPack wrote in post #5754751
Something else that just occured to me..

All ISO's above the base/native ISO are made possible by boosting the gain on the sensor right?

So ISO 400, 800, 1600 (maybe 200 depending on whether 100 is the base or not) are all 'fake' iso's made possible by boosting the gain of the sensor. If what i read above is correct, to get the 1/3 stop ISO's (the latter of the two 1/3 stop) why the need to boost above it and then pull it back again?

For example say you choose ISO 640, why does the camera boost to 800 and then pull it back? As they're all fake iso's and just variable strength of signal boost, why not just boost the gain enough to reach 640? Pushing it to 800 and then pulling it back makes no sense at all to me.

If that is indeed the case then i'm sure there must be a valid and no doubt scientific reason for it that I wont understand!

I'm just guessing here - I may be WAY off base...
I woud expect the "in between" speeds to work more or less like a linear volume control - base ISO is zero, a full stop above base, is one, two full stops above is 2, 2 1/3 stops above base is 2 1/3, 2 2/3 stop above is also linear.

I can't see why one can only boost in full stops, and then add 1/3 or go to the next full stop and subtract 1/3. Does not make sense to me.

Of course, I'm applying basic logic and assumptions to that which I actually know nothing about, for sure. Pure conjecture, here. Use at your own risk. Tell me I'm full of S&*I, and I'll agree (on this one, anyway...)

Flexipack also brought up a great question about the base ISO for the 40D possibly being 200 because the extended dynamic range locks out ISO 100. Could they be using some type of hybriding algorithm using the base ISO for light pixels, and the ISO 200 pixel amplification for the darker pixels? Ooooo - What magic, really, does Canon have up its sleeve?

Unless I missed something, nobody has actually agreed on a definition of "native".

How about this: a native ISO is one that is set by adjusting the gain of the sensor's amplifier.

By that definition, I *think* the native ISOs are 100, 200, 400, 800, 1600 in my 30D.

Interpolated ISOs would be the in between ones plus H (3200).

Is that a decent definition? I've never seen where Canon has used the term...

-js

(Sorry about this slightly off-topic question)

Gui: Since the difference between ISO 100 and ISO 1600 is 4 stops, and DPP (for example) only allows up to +2 stops of exposure correction, how did you boost the exposure in the ISO 100 shot by +4 stops? I once tried this myself, but I only boosted an ISO 400 shot by +2, since I don't know how to boost ISO 100 by +4... or did you just set RAW-tab EC to +2, and then modified RGB-tab curves so that it looks approximately as if still brightened up by additional 2 stops? Maybe I missed something.

I'm not disagreeing with you at all, just curious.

I think that there is only ONE native resolution by definition.

A monitor for instance may have a native resolution of 1920x1200 but you can display various resolutions on it like 1440x900 or 1680x1050 but it still has a native resolution, that is the physical number of pixels on the screen.

The native ISO is the level at which the sensor data is not being amplified.

I've been under the impression that that native ISO on most of Canon's modern cameras is ISO 200.

I may be wrong about all this and would welcome someone who knows more.

BTW, I recalled something Chuck Westfall had written regarding this. He didn't come out and say what the native resolution was but said this:

"ISO 50 can be helpful when you are trying to achieve a creative effect, such as a wide aperture to blur the background behind the main subject, for instance in portraiture. It can also be helpful when you are using studio strobes and you don't want to stop down the lens excessively, or in outdoor situations when you want a longer shutter speed to blur subject movement like the water in a waterfall. But if none of these situations apply, you are better off to use ISO settings in the 100 to 200 range in terms of overall image quality and maximum dynamic range."

Source: Chuck Westfall's Tech Tips http://digitaljournali​st.org/issue0804/tech-tips.html

gooble wrote in post #5754998
I think that there is only ONE native resolution by definition.

By whose definition? Yours? Canon's?

That was the point of my post. We need a common definition or this discussion is pointless.

The output of a CMOS photo cell is a very small voltage. Amplification is always required.

-js

number six wrote in post #5755039
By whose definition? Yours? Canon's?

That was the point of my post. We need a common definition or this discussion is pointless.

The output of a CMOS photo cell is a very small voltage. Amplification is always required.

-js

My definition? The definition of the word NATIVE in this context. Look it up.

Didn't you read my comparison of the monitor? To have multiple "native" attributes is an oxymoron.

gooble wrote in post #5755104
Didn't you read my comparison of the monitor? To have multiple "native" attributes is an oxymoron.

It's easy to have multiple native attributes. It's all about what level of amplification is set on the chip. These are all native to the chip and applied before the data is processed. The more the amplification the higher the ISO but all are still on the silicon, thus native to the chip. ISO's like 125 or 166 are some native ISO value with software processing applied as well. These then become interpolated ISO values or non-native.

There is a great article that discusses the chip architecture and how the chip works. Page 2 and page 10 shows a diagram of a single pixel and the associated circuitry. Page 6 describes how various ISO settings are set.
http://doug.kerr.home.​att.net/pumpkin/CMOS-APS_Sensor.pdf

gjl711 wrote in post #5752097
I use to be very ISO conscious as well always trying to get the shot at ISO 100. But the more I shoot at the higher ISOs, the less I see value of trying to keep it low. I pretty much have settled on ISO 400 as a starting point but don’t shy away from 800 or 1600 or even 3200. As DN says, noise ninja cleans it right up is I miss on the exposure.

This is a great link John.

There is also a plot for the 20D/30D sensors that was on dpreview last year - it is very similar in that the values of 160, 320, 640 seem to be a good choice to minimize noise. I've been using these values for over a year now.