initial notes on flash photography

Up until now, I've only been shooting with available light. The following are my initial notes on learning how to use the flash on my camera. I know I'll probably have to correct myself at some point in the future as I learn more about how to use the flash.

In automatic exposure mode, the camera assumes the flash is the primary light source in the photo. Since the flash only illuminates things up to ten feet away from the camera, everything else beyond ten feet ends up being really dark. This is what I've referred to as the "cave effect." This is what most point and shoot cameras do -- and what SLRs do when put in automatic mode.


Program Auto Exposure (P) mode. Camera chose: f/2.8 for 1/60 sec.


Aperture Priority (Av) mode. I chose f/2.8, camera chose: 1/4 sec.

By changing the camera mode to aperture priority, the camera assumes the flash is not the primary light source, but rather a foreground fill light. In aperture priority, I chose the aperture setting to be f/2.8. Since the scene is still dim, the camera chooses the shutter speed to be slower. This allows for the flash to "freeze" the motion that is in the foreground, while allowing for more light from the background to get into the picture. I think of how this works in terms of a piece of film: if there's something bright in the frame (something lit by flash), it will immediately burn into the film. If there's something dimmer in the frame (background light), it takes a little longer to seep in to the film. That is, the bright parts of the photo are exposed faster than the dim parts of the photo. The camera and flash (at least on my camera) calculates the flash power output and the shutter speed to make sure the foreground is not overexposed. Since the shutter speed is so long, one has to really hold the camera still or use a tripod (unless trying to do effects like streaking the background). However, if one is using a large aperture (let's say f/1.4, 1.8, or 2.8) the background will be thrown out of focus due to the shallow depth of field and any camera shake or motion blur in the background will be blurred out anyway.

The camera was set to ISO 400 in both photos and I used an older Canon Speedlite 380 EX as my external flash. The flash has a omni-bounce diffuser on it and is aimed 60 degrees upward toward the ceiling. Final note: sometimes when there really isn't enough light in the foreground or background, you have to use the flash as the primary light source. In that case, the photo will appear more like the first, rather than second photo above. Sometimes it's better to have a picture with cave lighting than to have no picture at all :)