On 10 Mar 2003 16:50:10 +0100, Christoph Breitkopf <chris@chr-breitkopf.de> wrote:

>"Bhup" <nospam@nospam.com> writes:

>> what does the iso settng on the as-17 actually do ?

>>

>> I thought the contacts on the as17 was sufficeent fot ttl flash

>> and thought the iso setting on the as-17 was a noyhing bit . correct me if

>> I am wrong

>>

>> I thought the camera tells the flash when to cut out the power? when it had

>> recieved sufficent light for the exposure.

>For modern 'normal' TTL flash, true. As the first Nikon body with TTL flash,

>the F3 works differently, though. The exposure calcuation is done

>within the flash - there are no electronics for TTL flash in

>the body. It is basically a direct wire from the light sensor

>to the flash connector. That's why the flash has to be told the ISO

>setting. F3 dedicated flash units sense this mechanically from the

>camera's ISO setting.

This also permits setting TTL fill-ratios, if the film speed

is enough below the 400ASA max to permit it; set the SC17

(or AS-7/17) ASA higher than the film speed by the amount

you want the flash to underexpose in TTL. Another trick that

works with the SC17 and F3-footed flashes (though this

prevents the ready light from lighting, and allows shutter

speeds above the synch speed to be selected) is to cover the

center of the three small contacts on the camera shoe, which

leaves the ambient-light meter turned on when the flash is

on...