One of the most common confusion which occurs with the Canon EOS flash photography is the fact that the Canon EOS modes like the Program (P ), Shutter Priority (TV) , Aperture Priority (AV) and Manual (M) modes handle flash illumination is different ways. This is especially so when the ambient light is not strong. This guide will give a brief run down of how the various modes work when the flash is activated. This guide also assumes that the FP mode is not turned on.



The Program (P) Mode:

The principle behind the P mode is that the camera will try to fix a high shutter speed to enable you to hold the camera without a tripod even though the ambient light is low. By doing so, you can avoid the "motion blur" effect on the image taken. It will operate in either by, when the ambient light is bright, assuming that you want to flash fill the fore ground subject matter. Thus it will meter the ambient light level then uses the flash at a low powered setting to fill in the fore ground. If the ambient light level is low instead, the P mode will illuminated the scene with the flash. It will also set the shutter speed at the camera highest as well. However picture taken in this mode will result in the background being dark.

Shutter Priority (TV) Mode

With this mode, the Camera lets you decide the shutter speed instead. It will decide on the aperture priority settings to suit the shutter speed that you have chosen to make sure that the exposure level is correct. The flash pulse duration will be decided by the flash metering system. In essence the Camera will always function under fill flash mode when in TV mode. This is the opposite of the "P" mode. The Canon EOS system will also indicate to you if the background is too dark. You will see this warning when the Maximum aperture settings begin to blink in the viewfinder. If this happens, you have to reduce the shutter speed and use a tripod stand to hold the camera to avoid motion blurring.

Aperture (AV) Priority Mode

With this mode, you can fix the depth of field (DOF) by adjusting the lens aperture. The camera will determine the correct shutter speed for exposing the background to the correct level. The metering system will decide also how long the flash pulse should be. You have to note that if the shutter speed is low, you will need a tripod stand to prop up the camera instead of using your hands to hold the camera. This is because at low shutter speed, your pictures will end up having motion blur. Just like the TV mode, the camera operates fill flash mode. There are several cameras which have the exception to this mode. The canon EOS10/10s and the Canon Elan II/ EOS 50 models has a unique function will lets you lock the X-Sync speed to the Shutter Speed.

M (Manual ) Mode

With the M mode, you will choose both the aperture and shutter speed of the camera. You will also decide the exposure level of the camera. With the flash metering system, the camera will determine the correct flash pulse to illuminate the foreground.