twoexposuretriangles When you add a flash unit to your image capturing you are actually making two shots that result in one: the first is of the ambient light, that is, the light that’s already available whether it is the sun, direct or reflected off snow, sand, water, or a wall, incandescent light bulbs (“tungsten”), or candlelight. The second shot is of what is illuminated by the flash. As you can see in the two different exposure triangles above, ISO and Aperture affect both of these shots, but shutter speed only affects how much ambient light is captured in the shot. The third corner of the flash exposure triangle, the one for our “second” shot, is for flash power, that is, the intensity of the light coming from your flash unit. If shooting in TTL (“through the lens”) or auto flash mode, then the flash’s TTL mechanism determines how much power to use in the flash. If, however, you are shooting in Manual flash mode (that’s “manual” on the flash, not the camera!), then YOU are determining how much power you want from the flash: 1/1, 1/2, 1/4, all the way down to 1/128 power depending on the flash you are using.

So, the normal workflow when setting up a shot using flash is to first determine the aperture at which you want to make your shot based on creative decisions or subject variables. Then, decide how much of the ambient light you want to be present in your final shot. If you're going for a completely black background or, at least, very dark one, then you will want to shoot with a fast shutter speed, possibly as high as your camera's sync speed. This is usually 1/200 or 1/250 for most modern digital SLRs. On the other hand, if you want to include ambient light in your image - perhaps you are working with a set or particular background material with a pattern that you want to be seen - then you'll want to use a slower shutter speed. This is trial and error until you get to know your camera, the lighting, and the setup. You might start at 1/60 and work from there. Regarding ISO, I generally start with my ISO set to 100, but it, too, can be raised to allow for more ambient (non-flash) light.

Now it's time to take your test shots. You do this with your flash(es) off so you can see how your selected ISO and shutter speed are affecting your ambient light capture. Once you are happy with the look of ambient light, it's time to turn on your flash and take a shot. After checking your resulting image, you may need to move your main light and reflector or second light depending on how your test shots came out.

So, always remember that you are actually taking two photos when shooting with flash: one that captures the ambient, existing light and the other that captures only the light from your flash. This fact gives you lots of flexibility in creating your vision in your image.

In addition to teaching scheduled photography classes throughout the year, I am also available to do one-on-one tutoring or small group lessons designed to meet YOUR needs and what you want to learn in the area of photography, using flashes, or the use of Apple products and software. Give yourself the gift of learning: http://www.infotor.com/photoclasses!