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MartyF81 Feb 27, 2007 3:30 PM

I tried doing a search, but the word "Program" comes up with too many hits! So if this has been answered already... I would appreciate a link!

Can someone explain what the difference between the Program AE and the Av Mode? What is the benefit of Program AE? I am really confused.

I have a Rebel XTi/400D


JohnG Feb 27, 2007 4:09 PM

Program mode basically is auto mode with exposure compensation enabled. The camera still selects what it thinks is the best shutter speed and best aperture to use but you have the ability to use exposure compensation. My guess is that EC will adjust shutter speed and not aperture (since you can run out of aperture to adjust more quickly than shutter speed). I don't recall if program modee auto selects ISO or not - experiment and see if it does or if you are allowed to set the ISO value.

In AV mode - you MUST select an aperture value and an ISO value. Given those two values the camera will select a shutter speed. If you use EC in this mode the camera will adjust shutter speed up or down by your EC amount.

So right off the bat a difference is in program mode you have no control over the aperture value but you have complete control in AV mode.

The only thing I'm not remembering is whether program mode allows you to change ISO or if it selects it for you. But a quick experiment should prove that out - put it in program mode and see if ISO selection is enabled.

MartyF81 Feb 27, 2007 4:32 PM

Manual says you can adjust ISO.

But it also says you can adjust Aperture, Shutter Speed, Exposure Comp on Program AE.

It says on the "Program AE mode" you can adjust Aperture, Shutter Speed, Exposure, and a million other things. When you adjust one of the first 3, the other 2 are adjusted for you to maintain exposure...

But isn't that what Av mode does? In Av mode when I adjust Aperture, the shutter is adjusted for me automatically right?

I am way confused....

Nagasaki Feb 27, 2007 5:30 PM

In program AE mode the camera selects a suitable aperture and shutter speed for the available light. You can then shift the program to give a different combination of aperture and shutter speed. If the light changes either the shutter speed or aperture or both may change without you doing anything.

In AV mode you select the aperture and the camera selects the shutter speed. This is different because you always select the aperture and the shutter speed will change if the light changes but not the aperture unless you decide to change it.

In TV mode you select the shutter speed and the camera adjusts the aperture to suit the light. If the light changes the aperture may change but the shutter speed will not.

Program mode is very flexible and suitable for most shooting situations but if you want to be in control of the aperture for depth of field of the shutter speed to capture motion or create blur then the AV and TV modes are better.


steve Feb 28, 2007 12:17 AM

When inaperture-priority mode, you select an aperture and the camera chooses an appropriate shutter speed. The main purpose of using aperture-priority mode is to control the Depth of Field.

When a lens focuses on a subject at a distance, all subjects at that distance are sharply focused. Subjects that are not at the same distance are out of focus and theoretically are not sharp. However, since human eyes cannot distinguish very small degree of unsharpness, some subjects that are in front of and behind the sharply focused subjects can still appear sharp. The zone of acceptable sharpness is referred to as the depth of field. Thus, increasing the depth of field increases the sharpness of an image. By usingsmaller apertures (higher f-stop values)you increase the depth of field.

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