Most flashes have a forward-facing photocell on the front for sensor-automatic mode (the photocell is the “sensor”). It’s usually about 3mm or 1/8” in diameter. This reads flash that’s reflected from the subject. You have to be careful to not block the sensor with your hand or camera strap. On my Metz 60-CT2, the sensor is on the center of the handle just below the flash head.
Fractional-stop fill flash is had by setting the film-speed indicator on the flash unit to faster film speeds (1/3rd-stop increments, obviously). Naturally, you shouldn’t change the ASA setting on the meter. I don’t think you can get fill flash increments finer than 1/3 stop.
So, if you were using an ASA 160 film and you want -1f fill flash, set the flash at ASA 320. For -(4/3)f, set the flash at ASA 400. For -(5/3)f, set the flash at ASA 500, and so forth.
Obviously you must use the aperture indicated on the flash unit for this to work properly.
Last edited by Ian C; 07-08-2012 at 04:29 PM. Click to view previous post history.