Confusion always results when users of Canon EOS camera tries to use the various modes available without trying to understand how they work. This is because the Canon EOS Camera has different modes like AV (Aperture Priority), TV (Shutter Priority), Program (P) and Manual (M) mode to handle its operations. The differences in they way they handle flash illumination is more obvious especially when the ambient light is low. This guide will give you a brief rundown on the various modes so that you will have a better understanding. We are also assuming that the FP mode of the camera is not turn on.

The P (Program) Mode

With the P mode, The Shutter speed is set to the highest possible speed to let you be able to hold the camera with your hands. You will also not have the problem of motion blur since the shutter speed is set fast enough to compensate for the low ambient light conditions. The P mode also functions when the ambient light is high. Under High ambient lighting conditions, the Camera will assume that the foreground will be flashed filled. Therefore, the output of the flash will be low powered. Conversely when the ambient light is low, the flash will be adjusted to give a higher output. The shutter speed will also be adjusted accordingly. But the picture will result in having a dark background.

The TV (Shutter Priority) Mode

Under this mode the camera will let you decide the shutter speed. It will instead choose an aperture priority to suit the shutter speed to ensure that the exposure level for the background is correct. The duration of the flash pulse will be determined by flash metering. In short, the camera always operates in fill flash mode under the TV mode as opposed to P mode. The Canon EOS system will also warn you if the background is too dim. This will be shown when the maximum aperture value of the camera lens starts to flash in the viewfinder. When this occurs, you should slow down the shutter speed. You will also require a tripod if you wish to avoid motion blur.

AV (Aperture Priority) Mode

Under this mode, you will be able to fix the depth of field by setting the lens aperture. The camera then decides the appropriate shutter speed to expose the background to the right level. The flash pulse duration will be determined by the metering system of the flash. However note that, if the shutter speed is set really low, you will need a tripod to avoid motion blur. As in TV mode, the camera will work in flash fill mode as well. The only exceptions to this are the Canon EOS 10/10s and Canon Elan II/ EOS 50 models. These cameras have a custom function which allows you lock the shutter speed to the X-sync speed.

M (Manual ) Mode

When you use the M Mode, you will determine the aperture and shutter speed of the camera. The exposure level will also be decided by you. The camera will just determine the correct flash duration to illuminate the foreground using the flash metering system.