Program mode

[peachy]

Not sure if this has been asked before... When the camera is in program mode, how does it decide on the settings? I know that in the general sense, it chooses an aperture and shutter speed that will expose the image properly. But how does it decide how much light to let in by each method? What I mean is, how does it decide to use a slightly slower shutter speed instead of slightly larger aperture to compensate for lower light? Any ideas? Thanks... just curious

[RichardTaylor]

See post #6 in this thread.
How do you think the 7D chooses the ISO "program line?" - Canon Digital Photography Forums

According to my EOS 1000 (film SLR) manual it chooses the best shutter speed/aperture combination, taking into account the lens focal length (1/the focal length for the shutter speed) and the light available.

The graph is similar to those in the link given.

[Doug Pardee]

Originally Posted by peachy

When the camera is in program mode, how does it decide on the settings?

As shown in the graphs and stuff on that other thread:

In dim light, the aperture is wide open and the shutter speed is set as necessary.

As the light increases, the shutter speed gets faster. Once the shutter speed reaches about 1/f, the camera begins to alternate stopping down the lens by one increment (usually 1/3 stop) and increasing the shutter speed by one increment.

As the amount of light continues to increase, it's possible (especially at high ISOs) that either the shutter speed or the aperture will max out. At that point the camera has to switch to adjusting only the other setting.

Simple enough?

The main point of all of this is: you probably don't want to use P mode. It's far too liberal with adjusting the aperture, letting it go very wide or very tight when most photographers would simply adjust the shutter speed and use a better aperture. The program mode not only doesn't have intelligence, it's downright stupid.

[PhotoNewt]

Originally Posted by Doug Pardee

...The main point of all of this is: you probably don't want to use P mode. It's far too liberal with adjusting the aperture, letting it go very wide or very tight when most photographers would simply adjust the shutter speed and use a better aperture. The program mode not only doesn't have intelligence, it's downright stupid.

What you don't want to use is the full auto mode (the green [ ] on most xxD and xxxD models) of the camera as this usually leaves you with little control over the camera selected parameters.

The P mode instead makes an "educated" choice of photographic parameters, if you don't like the selected aperture/shutter combination, it can be easily changed on the fly using the program shift function (the wheel behind the shutter release button) until a more apropriate combination is selected. BTW, on P mode you also have access to all other creative parameters offered by the camera, most of those are not accessible on the full auto mode.

[Doug Pardee]

Originally Posted by PhotoNewt

The P mode instead makes an "educated" choice of photographic parameters

The P mode on Canon DSLRs is not "educated"; it's willfully ignorant. It makes terrible choices under most conditions, opening the aperture too wide or stopping it down too far.

About the only thing that you can say for P mode is that if it's possible to get a usable exposure combination at all, P mode will come up with one. On anything above the Digital Rebel series, you can accomplish the same thing—and with much better control—by using Av mode with Safety Shift.

[peachy]

I usually use Aperture priority, so Program mode doesn't come up too often for me, I was just curious. Thanks for the info!