Here is a picture of my setup.

enter image description here

The remote flash fires correctly but I don't know why Master flash is firing too? or maybe is it just pre-flash? But it looks pretty bright to me, not sure if it is pre-flash.


1 Answer 1


You are using TTL, which means all flashes have to communicate with the camera and there has to be a preflash to determine the flash output.

The process is something like this:

  1. preflash: let every flash fire at a certain power level
  2. meter the exposure during preflash and calculate if they should have more or les power during the actual exposure
  3. actual exposure: communicate to each flash at what power level they should fire (depending on possible group ratios, etc...)

The master has to fire whenever the slaves should fire, which is either to tell them to do the preflash or how to do the actual flash.

  • \$\begingroup\$ So it is pre-flash from the Master, Can I tilt the head of the master in some other direction? or has to point to the subject? \$\endgroup\$
    – Brandon
    Commented May 17, 2015 at 13:58
  • \$\begingroup\$ Is the flash of the master unit visible on the subject? that would indicate that it is not a pre flash. Yes, the best thing to do is to point the master flash towards the slave unit in order to ensure a line of sight connection. \$\endgroup\$
    – null
    Commented May 17, 2015 at 14:01
  • 2
    \$\begingroup\$ Note that the last control flash does happen with the shutter open so in situations where the master flash is very close or when there are mirror surfaces in the subject, it can show on the subject. \$\endgroup\$
    – mattdm
    Commented May 17, 2015 at 15:05

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