5D mkiii records incorrect ISO?

[Manni141]

Hi guys,

First post here. I've just been shooting with the 5D mkiii using ML and noticed a potentially big issue.

I usually use native ISO's eg. 160, 320, 1250 etc. But when I set it, the ISO reads differently on the ML globaldraw menu. For example, if I set the ISO to 160, it will read as 200 on globaldraw display (the display that comes up on LiveView). My images tend to have more grain than usual which has me thinking that it is being recorded with a higher ISO than I set.

I have tried setting the ISO both in camera and with ML. Same results. Anyone else have the same issue?

Thanks

[dmilligan]

My images tend to have more grain than usual which has me thinking that it is being recorded with a higher ISO than I set.

All else equal, higher ISOs have less noise (per electron), not more (otherwise it would be pointless to have them).

When you use ISO 160, the camera actually uses CMOS ISO 200 and pulls it down some. This is why the ISO 160 multiples appear to have less noise and more DR. They are actually "pulls" of higher ISOs.

If you are recording raw video, then this is expected, the intermediate ISOs do not affect the raw data coming off the sensor. So only multiples of 100 are possible. You can achieve ISO 160 by shooting with ISO 200 and pulling it down 1/3 stop in post.

Further reading:
http://www.magiclantern.fm/forum/index.php?topic=10111.0
http://clarkvision.com/articles/iso/
http://www.clarkvision.com/articles/evaluation-canon-5diii/index.html