Manual mode auto iso question

Started Jan 7, 2013 | Discussions thread
Johanfoto
Senior MemberPosts: 2,928
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Re: Manual mode auto iso question
In reply to Matt Daddy, Feb 19, 2013

Matt Daddy wrote:

I want this too! I've had a 6D for about a week and I really like it. I upgraded from a 20D, so the 6D has tons of features that I never had before. Walking around museums taking pictures of my son doing things, and just "mood" shots of various scenes in the museums, I'm finding I really like the manual mode with auto ISO combination. However, sometimes the metering makes the picture just a bit too bright or too dark (usually in low-light situations, the picture comes out too light) so I'd like to adjust the exposure by 1/3 or 2/3 stops. Of course I can do it later processing the RAW image, but I'd rather not have to go through the extra effort. It seems like it would be so simple to do in the software, I don't understand why they don't allow exposure compensation in M mode with ISO set to Auto.

I believe there is a more or less 'philosophical' reason. The exposure is the amount of light which falls on the sensor, and so the only way you can change the exposure is by changing the aperture or the shutter speed. Changing the ISO does not change the exposure! The ISO value determines how the sensor reacts to a given exposure, so technically a change in ISO is not an exposure change, but a 'signal processing change'. That is why Canon engineers feel that 'exposure compensation' with manual exposure settings is like a square circle: It can't exist.

Of course for a photographer this is just technical hair-splitting. We are only interested in the practical implementations and indeed some kind of 'Auto ISO compensation' would be very useful, whatever you would call it. But unfortunately Canon engineers are technicians, not photographers.

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