Fri 12-Oct-12 03:59 AM | edited Fri 12-Oct-12 11:56 AM by kentak
>Thanks, > >I couldn't agree with you more. I was just testing out the >camera and that's the one mode that isn't making sense.
It makes sense if you understand EV (Exposure Value) and the chart on page 315 of the manual.
See "Exposure Value" in Wikipedia for an explanation of EV. I like to think of EV as one way of objectively describing the amount of light illuminating a scene.
Program mode is an automatic *exposure* mode that sets an aperture and shutter speed to give a technically correct exposure for a given amount of light based on a predetermined "program." That program is described on page 315 of the manual.
For example, one of the charts in the Wiki article describes the EV of a "heavy overcast" daylight condition as EV 12 (@ ISO 100). The chart on page 315 shows that P mode would set the camera for an aperture of 5.6 and a shutter speed of 1/125 in that lighting situation. This assumes the meter is reading average subject and not one that is at the extremes of light or dark reflectance.
As the lighting conditions become darker, the program adjusts both aperture and shutter speed to attempt to keep a correct exposure, i.e., the aperture opens up and the shutter slows down. The opposite applies if the lighting conditions get brighter.
A nice feature of P mode is that you can vary the program if you don't like the aperture or shutter that has been selected. In the example above, if you would rather have an f/stop of f/4 to get a little more background blur, just turn the command dial while the meter is active until f/4 is selected. As you adjust the aperture, the camera automatically set the shutter speed to maintain a correct exposure.
In general, P mode is most appropriate if you want the camera to set a correct exposure when you are not too concerned about needing a specific aperture or shutter for a desired effect. When those become more important, you should probably be using A, S, or M mode.
P mode differs from Auto mode in that it automates only the exposure. Auto takes over focus modes and focus points and flash firing, even to the extent of popping up the flash automatically if it is needed.