T2i intermediate ISOs

[shaocaholica]

The difference between ISO200 and ISO160 isn't controllable be the user. Its done on camera. If you underexpose, it won't help. Setting exposure compensation to something probably won't do anything either and wouldn't be worth the hassle.

[macgregor]

Use native ISOs for best image quality. Native being 100, 200, 400, 800...
Intermediate ISO gains are done by software, therefore reducing highlight dynamic range. Sure there might be a bit less noise at 160, 320 and so on, but highlights clip earlier.

People shooting at ISO 160 are loosing 1 1/3 of a stop in highlight detail (compared to ISO200 with HTC ON). That´s actually a lot.

[berylium]

Macgregor:

That is very interesting. Is there a test that confirms this?

I am suffering from 7D envy when it concerns less noise.

[macgregor]

Copy/paste from previous posts:

It´s being common knowledge that at least in lower Canon models, intermediate ISO gains are done by software (when the camera or your PC converts from RAW-RGB): for all of the +2/3rd ISO stop levels, they are actually using the next higher full-stop ISO level, and dropping the EV by 1/3rd after the A/D conversion!

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
and so on

You can find a lot of charts showing this. like this one http://forums.canonphotogroup.com/showthread.php?t=2541

So yes, ISO160 has less noise than any other ISO setting BUT the dynamic range is shifted (highlights clip earlier).

I just did some test today with a 5D. Exactly as expected, the intermediate ISOs clip highlights detail earlier (1/3 of a stop). And HTP gets you another stop. So for example, shooting ISO 400+HTC gives you +1 1/3 stops more in highlight detail compared to ISO 640 given the same mid grey exposure.

[greeches]

^Thanks Macgregor. That is what I was trying to convey, but with not-so-great language/wording.

Thanks for clearing it up!