In the good old days of photography, you put in a roll of film and
then had two variables that you could change to control exposure,
the f/stop and the shutter speed, for the next 12/24/36 shots.
Depending on which generation of film camera you shot with, you
would have the following options:
1) M - Manually set the aperture and the shutter speed.
2) A/Av - You set the aperture and the camera automatically sets the shutter speed for you.
3) S/Tv - You set the shutter speed and the camera sets the aperture automatically.
4) P - The camera sets both the aperture and the shutter speed automatically. (There are lots of versions of "Program" mode that tell the camera to try to do different things, but in all cases it handles both settings for you.)
ISO is a constant in all these cases. This makes sense as there was no practical way to change film between each shot (and yes, I'm talking about 35, 120 or other roll film cameras. Don't be a smart ass and say that if you shoot with 4x5 or other sheet film formats you can change ISO with each shot.)
With digital, things are different. The sensor in the camera can be setup to read at any available ISO at any time. Between every shot if you wanted to. So, the question becomes, why not add option 5 to the above list. Call it "PISO".
All three of the variables, f/stop, shutter speed, ISO would be set automatically in this mode. Theoretically, at least some point and shoots do this if you set their ISO to Auto. So, why not kick it into digital SLRs. I'll grant you that I would almost never use it with my main camera. I keep a point and shoot handy when I don't want to think about anything. But, it sure would be a nice option to have, especially when shooting for fun in dramatically changing lighting conditions, or when you've had more than your fair share of drinks.
– Tags: tagPhotography