[shuttertalk]

I notice that a few of the Digital SLRs out there have the lowerst sensitivity of ISO200 only. Seems rather strange, doesn't it? Does that bother anyone? Can you live without ISO 50?

[adam]

D70!

I've never played ISO50, is there any firmware hack that would let me do such a thing?

[Don Schaeffer]

I typically use iso 100. In the Winter we get so little light I switch to iso 200. Everything higher is much noisier.

[Toad]

Lower ISOs are basically used to decrease color noise. They do it at the expense of shutter speed. For a given aperature, as your ISO lowers - your shutter speed gets slower. If your DSLR has mastered noise to the point where they do not need to provide lower ISO settings - why would you want to use a lower ISO?

Of course if the DSLR has NOT mastered noise at ISO200 - that is another issue altogether.

[adam]

If your DSLR has mastered noise to the point where they do not need to provide lower ISO settings - why would you want to use a lower ISO?

there's no need for a lower ISO if the DSLR has mastered noise!

Was wondering if ISO50 would give me longer battery life haha! It would use less electricity for the sensor, but more for the shutter (keeping it open for longer)

[Toad]

Ha ha - that's good...yes the ISO 50 might result in lower battery use - but you probably wouldn't be able to measure the difference...

[adam]

Actually at first, when I mentioned about ISO 50, I said it thinking that it would mean less noise, then you pointed out that if the camera has mastered noise at the ISO, then there's no need to shoot at lower ISO Which made me realise that ISO100 isn't noisy, so there's no need for lower.
I think that ISO50, would let me do long exposures with less noise that if I did it at ISO100? Is this true?

[Toad]

Yes - that is true - typically lower ISO means less noise and finer grain.

[pai]

sometimes you want to control both shutter speed and depth of field, so the only thing you can vary to get the right exposure is your iso? (ok nd filters )

so say you wanna shoot in bright sunlight, at a slower shutter speed, but with a wide aperture - you might need to go to a lower iso speed to do it i think.

i guess one alternative if you're shooting in raw is to use manual mode and then lower the exposure in postprocessing... i'm not sure if all cameras work this way, but i think with my a2, the iso setting doesn't actually change the sensitivity of the sensor. instead, the sensor has a native iso setting (around 125 i think?) and to get pictures at other iso ratings, a multiplier is applied to the data...

[adam]

Yes! thats what I also wanted to mention, about using lower iso to have longer exposures hehe

[Toad]

Yes - you are both quite right - those are excellent reasons for having access to lower ISOs.

Pai: I didn't know that about the A2 - I will have to read my manual and see what I can find out.

[slejhamer]

Pai: I could be wrong, but given that the A2 uses the same Sony-designed 8mp chip as the Sony F828, Oly 8080, Canon Pro1, and Nikon 8700, it's unlikely that there is a different methodology driving the ISO sensitivity.

But you are correct about the "multiplier." Digital camera light sensitivity (ISO) is actually an amplification of the sensor's analog output prior to analog-to-digital conversion. So both signal and noise get amplified at the same time.

The guitar players here should find this familiar - turn up your pre-amp's gain or overdrive setting and what happens? Distortion!

Rock on!

[pai]

good comparison with the guitar amp

i seem to have lost that article on ax sensor iso... will post a link when i find it.