Canon EOS Flash Photography Explained
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 P (Program) Mode
Under the P mode, when the ambient light is low, the camera will be set to a high shutter speed to enable you to use the camera without a tripod stand. This is to enable you to avoid “motion blur” even though you are holding the camera with your hand. The P mode will work when the ambient light is low or high. When the ambient light is high, the camera makes the assumption that you will flash fill the foreground. Thus the flash will be low powered. If the ambient light is low, the camera will under the P mode will set the flash and the shutter speed appropriately to give the best possible result. Having said so, pictures taken under this condition will normally have a dark background.
The TV (Shutter Priority) 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.
AV (Aperture 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
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.