Andrew M. Moore wrote in message <65hd52$17p@bronze.lcs.mit.edu>...

>I have a basic question regarding a Nikon SB-26 flash unit that I
>recently purchased. I'm using a Nikon 6006 body, FYI.
>
>When I use the external flash in through-the-lens (TTL) mode, why must
>I tell the flash unit which aperture I am using? If the TTL sensor
>inside the camera is shutting off the flash only when it has received
>enough light, I don't understand why the flash unit needs to know
>anything about aperture or subject distance. It seems to me that if I
>use a relatively small aperture, the TTL sensor will simply keep the
>flash unit turned on longer, until it has received the proper amount
>of light for a proper exposure.

Why do you think you need to set the aperture on the flash...?
If you are using a non-AF lens, the flash display of aperture
will not follow the aperture changes made on the lens, but the
display is for information purposes only when the flash is used
in TTL mode (and it can be used to see the available flash
distance range when the ASA and aperture settings are given).
As long as you are likely within the useable range of the flash,
just shoot away and ignore the display when in TTL mode...
(that is, until you see the ready light blink...;-).
Hope This Helps
David Ruether - http://www.fcinet.com/ruether