I recently acquired an SYK-3 optical flash trigger to experiment with off-camera flash with my Sony a100, using the on-camera flash to trigger the units. To avoid triggering the off-camera flash too early, I needed to disable or turn off the pre-flash (both TTL and ADI have it). However, there is no setting on the a100 (and, as I could tell, from the a200, etc…). One solution, of course, is to buy an external flash (set on Manual), to buy an IR flash trigger, or to go with a radio wireless solution — none of which was cost effective for me at the moment.
Another solution that people had was to set the flash to rear-sync and to make the shutter-speed somewhere in the area of 5 seconds long. In this situation,
- the pre-flash will trigger the optical sensor
- the shutter will now open for 5 seconds, allowing the off-camera flash to charge again
- the camera flash will go off again just before the shutter closes, this will trigger the optical sensor while the shutter is open
The problem here is that the long shutter will create optical effects that may not be desirable to you.
However, I found a new solution!
- Set your camera to a have a 2-second delay in the timer. In this mode the camera will flash the pre-flash at the beginning of the 2 second timer, so….
- If you, cover the camera flash (or the optical sensor) with your hand during first the first flash, you will avoid the pre-flash trigger. Also, the shutter will not be open during the 2 seconds, which will avoid undesirable exposures.
- Uncover the flash/sensor
- The flash will trigger normally, while the shutter is open
This is admittedly a strange workaround, but it solves the problem without buying additional hardware. Good luck.