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Originally Posted by PhotoDave
You bring another question to mind... I have a D70 and am using an SB800. When the camera is set to Manual and I have the shutter and aperature set as desired, how doe sthe flash work whe in iTTL mode? Manual is cut and dry - I got that, but what about the TTL or iTTL modes? WIll the output of the flash be dependant upon the shutter, aperature and distance reported by the camera or will the flash intensity be based on the spot metering (i.,e. the models face or torso, hence changing the distance calc fo the exposure).
I Hope that question made sense anyway  |
TTL simply means that the camera is measuring the amount of light reflected off of the film or digital sensor. When the camera thinks that the amount of exposure is correct (enough to render 18% gray) it quenches the flash. iTTL takes distance information from the lens and factors that into the equasion. But that only works if the flash head is in the forward position, because the camera then knows the distance from the front of the flash to the subject. If the flash is set to bounce, the camera doesn't know how far the light has to travel to reach your subject.
Whenever you leave a part of your exposure solution up to the camera you're introducing some amount of variability. This is fine in many cases, especially with Nikon 3D color matrix meters. You won't find a more consistent and predictable in-camera meter. If you shoot enough (and pay attention) you will learn how your camera behaves in various situations and will learn to compensate. But meters can be fooled and you might find out that every frame is exposed just a bit differently. If you have the time to evaluate and meter your environment, you can knock out shot after consistent shot. Then you can stop worrying about what the exposure looks like and start concentrating on the model's pose, expression, and the scene in general. You'll be able to catch those fleeting moments you would have otherwise missed because you were chimping to check exposure.
-Chip