Quick one... optical slaves that handle preflash

[alan_potter]

Would some kind soul please remind me where I can find the brand of optical slave that can be taught to ignore preflash? It's slipped my mind...

Many thanks,

regards,
/alan

[Tom Camilleri]

Would some kind soul please remind me where I can find the brand of optical slave that can be taught to ignore preflash? It's slipped my mind...

Many thanks,

regards,
/alan

B&H has them. There are several brands- Wein is one.

[SkipD]

When I was starting to play with off-camera flash while using my Canon PowerShot G2, I bought a Wein "Digital" Peanut slave that will trip what it's connected to on the second flash burst that it sees.

However, the more I played with it, the more I found out how useless it (or anything like it) really is. The "Digital" Peanut slave merely stays tucked away and will probably never see service again. Why? Read on....

The only reason a Speedlite (or the built-in flash in your camera) emits a pre-flash (which it does when in ETTL mode but not in Manual mode) is to determine how much light will be needed for the main burst to make the image. In other words, the camera and flash are working together to establish the exposure for the image you are making.

If you merely add another remote flash with an optical slave such as the Wein "Digital" Peanut, you can get the remote flash to trip at the same time as the main flash from the Speedlite. However, assuming that the remote flash is also illuminating the main subject, the result will be overexposure. Why is that? It's because the camera "knew" nothing about the extra light source and calculated the exposure based on the pre-flash from the Speedlite. It's sort of like measuring the ambient light on a scene with a meter and then turning on enough lights to double the illumination before taking the shot (but not changing the exposure control settings on the camera).

There is only one way that I can imagine using a remote flash coupled to a Speedlite which is working in ETTL mode is to fill the background with light. As long as the remote flash does not add illumination to the foreground subject, the foreground subject should be properly illuminated by the Speedlite.

The best way to use a Speedlite with remote flash equipment is to have the Speedlite and the camera both set to manual exposure control modes. This way, you can trigger remote flash units with conventional optical slaves. You will need to use a meter to measure the light from the combination of flash units or do a set of trial-and-error experiments to determine the exposure settings for the camera.

[alan_potter]

Thanks for the pointer, Tom.

It was indeed as a background illumination that I was considering trying this kit, but I shall bear your concern in mind, Skip.

Thanks again,

regards,
/alan