ISO Settings

[dje]

I have a rather technical question regarding ISO settings for digital cameras. I understand the ISO concept in the digital world and also the analogy to film photography however my question is this

Are there standards which define ISO settings in a digital camera or for a sensor ? It seems to me that the ISO setting is basically a sort of analogue gain setting which determines how much amplication is applied in the sensor. As every sensor model and every camera model is different, how is the ISO setting defined or standardised so that we know that when comparing the ISO performance of different sensors/cameras we are comparing apples with apples.

Secondly, as the same ISO scale is used for digital as film, how are the two correlated or related ?

[Colin Southern]

Hi Dave,

I'd suggest that it's not so much the standardisation of the ISO that is important as it is the standardisation of the sensor performance / amplifier combination - so long as a Canon @ ISO X produces the same exposure as a Nikon @ ISO Y for the same illimination, do we really care if the ISO itself is standardised (although I suspect they would all be similar anyway).

If you want to compare ISO performance, pop along to www.dxomark.com and get more info on any camera than you'd ever want.

At the end of the day though, high ISO performance is often grossly misunderstood - in essence there are two things I think people need to be aware of ...

1. With each doubling of ISO (ie a "stop") in essence you're losing 1 stop of dynamic range (as the camera is in essence throwing away a stop from the top of it's range by under-exposing, and then moving everything else up) (essentially under-exposing, but adjusting with an analog amplification, not a digital manipulation - but the net result is that the noise floor is moved up as well, and thus the available dynamic range is decreased. At high ISOs you could well be down to only a handfull of stops of DR.

2. I think people worry far too much about high ISO noise - so long as the shot isn't under-exposed (thus wasting a DR that's scarce enough as it is), and providing the shot isn't excessively cropped (thus making the noise "larger") then my suggestion is to - in essence - not worry about it. In most cases you won't see it in a real-world print or inline image - people only ever freak out when they look at it at 100% on their monitors.

With regards to film -v- digital ISO - yes - the concept is the same, but the response curve is completely different between film and digital anyway - so once we get past the "concept", it's probably a bit of a moot point.

Hope this helps

[inkista]

Seriously. You're asking if ISO has a standard?! [facehands] ISO is the short name of the International Organization for Standardization (and no, ISO isn't an acronym). All their standards are ISO #:year of last revision. The one for digital sensor speed is ISO 12232:2006. Color negative film speed is ISO 5800:1987, B&W negative speed is ISO 6:1993, and color reversal speed is 2240:2003. The one for flash hotshoes is ISO 518:2006. Tripod connections are ISO 1222:2010. A lot of photographic gear works together because of ISO standards.

Wikipedia actually has a pretty good article on film speed that descibes most of the methods of determining film and digital sensor speed.

[dje]

Colin

Many thanks for your response. I had a look at the DXOMark site you referred to and it seems to have a wealth of information which will take me some time to digest. However I did pick up from that site in the glossary of terms that digital camera ISO settings are covered by ISO standard 12232. I should give myself a clip over the ear for not searching the ISO standards in the first place . Now I need to research that standard.

Your point about the relation between ISO setting and DR is a very interesting point which hadn't occurred to me.

Regards
Dave

[dje]

Kathy

You'll see from my response to Colin (which I posted probably whilst you were going to print) that I've acknowledged that it's red faces for me. Sometimes you cant see the wood for the trees ! And yes I'm looking at the Wiki article now.

Dave

[inkista]

You'll see from my response to Colin (which I posted probably whilst you were going to print) that I've acknowledged that it's red faces for me. Sometimes you cant see the wood for the trees ! And yes I'm looking at the Wiki article now.

Hey, no worries. I sometimes forget that not everybody's in corporate America and having iso 9000 "quality" procedures rammed down their throats. For a lot of photogs, film/sensor sensitivity/speed is the only ISO standard they run across.

[Colin Southern]

and no, ISO isn't an acronym).

Looks like there are two people in the world who know that!

[Colin Southern]

Colin

Many thanks for your response. I had a look at the DXOMark site you referred to and it seems to have a wealth of information which will take me some time to digest. However I did pick up from that site in the glossary of terms that digital camera ISO settings are covered by ISO standard 12232. I should give myself a clip over the ear for not searching the ISO standards in the first place . Now I need to research that standard.

Your point about the relation between ISO setting and DR is a very interesting point which hadn't occurred to me.

Regards
Dave

Hi Dave,

No worries.

In photography there are a lot of "in theories" - and often the "practice" is very different, for a variety of technical reasons.

With regards to High ISO performance, there are a number of competing issues ...

1. Newer models of camera tend to have higher pixel densities, and the higher the pixel density (for a given technology), the higher the noise ...

2. BUT ... technology doesn't stay the same ... and better technology improves base sensor noise characteristics - so the two offset each other to a degree

3. BUT ... consumers are also demanding better low-light capability - and that means higher ISO modes and thus more noise ...

4. BUT ... they're also getting better at in-camera noise reduction, so again it offsets this increase ...

5. BUT ... (lots of buts aren't there) the in-camera noise reduction is usually only applied to in-camera generated JPEGs, not RAW captures - and of course RAW captures give us many other advantages (although less at high-ISOs I believe)

So lots of things going on - in theory people are drooling over some of the high-ISO shots that they're seeing, but in practice they're not getting the same results because they're shooting RAW. Bottom line is - in real world photographs - it really doesn't make a lot of difference most of the time.

It's also been said high-ISO performance is only for those who don't understand flash -- and there's often more than a grain of truth in that too

[dje]

Hi Colin

I agree with you about the use of flash. I've seen some wonderful indoor shots taken using flash by a photgrapher who really new what he was doing (ceiling bounce etc). It all depends where the light is coming from and you don't always have much control over that without a flash in a low light situation. I suppose it's horses for courses and it depends on the subject. I know my grand-kids won't sit still for 1/400th sec let alone for the relatively slow shutter speeds you often need for non-flash low light photography!
Dave

[Colin Southern]

I've seen some wonderful indoor shots taken using flash by a photgrapher who really new what he was doing (ceiling bounce etc).

Hi Dave,

Actually, ceiling bounces usually give what I call "office lighting", which isn't very flattering - Side bounces usually work better as the give a nice direction to the light

Horses for courses of course. but personally, I find that low-light people shots usually aren't that great. There are exceptions of course, but often it's not directional, which usually makes for a better photo.