d20: switch off preflash?

[Stefan_Randlkofer]

although i am afraid i already know the answer: is there any chance to switch off the preflash in manual mode to be able to trigger oldfashioned slaves ?

[Michael_Price]

Not unless you have a flash that does into manual mode. I can put my 580EX into manual mode 1/64 power to trigger the studio strobes.

[Doug_Kerr]

Hi, Stefan,

[ QUOTE ]
is there any chance to switch off the preflash in manual mode to be able to trigger oldfashioned slaves ?

[/ QUOTE ]
If you are speaking of the onboard flash, and the Canon EOD 20D, as far as I know, on the 20D the onboard flash (if we allow it to give an actual "shooting" flash at all *) always operates in the E-TTL II mode, in which a metering preflash is always given.

* By this I allude to the fact that we can, with C.Fn05=1, set the onboard flash so it will not fire even if erected. The purpose of this is to allow us to use the onboard flash to give its horrid AF assist barrage but not participate in exposure. (The setting has the same efect with respect to a dedicated external flash, in which case of course the AF assist emission is not a white barrage but a red/near infra-red emission.)

If we are using an external flash such as the 550EX or 580EX, it can be put into its manual mode, in which case no metering preflash is emitted. As Michael Price has noted, in that mode the output level can be adjusted, so as to control the balance of illumination between the master and teh slave flash units, including to make the contribution of the master to the exposure negligible.

There are optical flash slave "receivers" which can be "programmed" to ignore the metering preflash. I do not know of any flash units having an integral optical slave capability that can do this except for one specialized Vivitar unit, which is not otherwise very versatile.

Best regards,

Doug