Canon 155 A - Manual (Page 11)

light as soon as the flash unit determines
sufficient light was reflected from the sub­
ject to the unit’s photocell.
There are three conditions in performing
automatic flash photography.
1. Set the 155A to the film speed of the
film to be used.
2. Set the shutter speed to the X synchroniza­
tion speed (when using cameras other
than the Canon A-1, the AE-1, the
AT-1 or the AV-1).
3. Decide the aperture to be used (and, with
cameras other than the Canon A-1 or AE-1,
set that same aperture on the lens aperture
ring).
If the above three conditions are fulfilled,
then all there is left to do is to switch the
flash on, focus and release the shutter.
When the Speedlite 155A is used on the A-1