| From: [EMAIL PROTECTED] (Tom Robertson) | Subject: EOS Canon 550EX Slave vs Master Flash ratio | | Here is what I am trying to do. I want to place one 550Ex flash to one side | of my subject and let it be the main flash. I want to use the second 550EX | on my camera as a fill flash. I am trying to do this and maintain ETTL. | The on camera flash is set as the master and the other flash as slave which | is my main flash. in other words I would like to set the ratio of the on | camera flash to anywhere from 1/4 to 1/2 of the slave unit. It would appear | by reading the manual that the A:B flash ratio only applies to two flashes | that are acting as slaves. Any way I can do this and maintain ETTL | metering. I am trying to preclude having to use an external flash meter. | | The camera is a Canon EOS-1V. Easy. Be aware of the following points: 1. The master flash (by definition, the one on the camera) is automatically a member of group A, although you can switch off its exposure flash if you want to. It is special only in that it emits the flash ensemble control signals from the camera body. Other than that, it is just another member of group A--sort of like the concertmaster in an orchestra. 2. Set the 'main' light slave or slaves to group B. 3. The first number in the A:B ratio is for A and the second one is for group B. Therefore, choose 1:2, 1:4, etc. to get the main/fill balance. 4. The flash exposure control will give you the desired ratio on the subject, automatically compensating for differences in distance, reflector type/size, and basic output capacity of the various flash units--up to the point where one or more of them cannot furnish as much light as the camera body determines is needed from that group. Therefore, you don't need to do any mental calculations of distance and so forth. Of course, you have to choose the setup so that the flashes have enough output to get the exposure you need, and you still get to make all the decisions on _how_ to light the subject. E-TTL ain't that smart, of course! If you want a bit more flexibility, you can go off-camera with all your E-TTL slavable flash units (at this time, 550 and 420 EX's) and put the ST-E2 transmitter on your camera. This will give you A:B ratio control but, alas, not group C control (only the 550EX will do that). * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
