caporip wrote:
I meant the ratio control. It can, according to the manual control two groups with ratio control the 58 has to be on camera but the off camera flash can be a 56 but only one off camera can be used. I have to admit ive not experimented much with this but plan to soon.
I don't know where you got the 'only one 56' - top of page 69 says clearly 'you can use several off camera flashes at the same time'.
Here is an example with the 5600, 3600 and 42 all in a row, being wirelessly controlled using mode CTRL2 via Custom Setting CO3 on the 58, which is attached to the camera and used as a bounce flash controller. The two-group ratio possible is only between the camera (CTRL) and the remote flashes (RMT). The 42 flash is always in the RMT group, and can never be assigned to RMT2; the 56/5600 and 36/3600 are also always in RMT group but can only be fired with the controller set to CTRL not CTRL+ (you get CTRL mode as stated above - adjust Custom Setting 03 to CTRL2, and the plus sign will disappear from the CRTL+, meaning you are now in CTRL mode for two groups only - on-camera and off-camera).
The controller's ratio has been adjusted here to change the level of bounce flash, relative to the fixed TTL output of the remotes. Each remote will give power in proportion to its GN rating. The 56 and 36 make a natural 2:1 lighting ratio, and the 56 with 42 is a bit closer. It's easy to work out - think of 56 as enough light for f5.6 when the 36 gives enough for f3.6 and the 42, for f4.2 - since they use slightly different coverage angles to compute their powers, it is not strictly accurate, but enough to help you get a working lighting ratio without needing further controls.
When the 42 is used with an additional external 58, is always in the Group 'RMT' and the controller is always in the group 'CTRL'. The extra 58 can be in 'RMT' or 'RMT2' groups, but never also in 'CTRL'. Further 42s can not be in 'RMT2', you must have TWO 58s to be able to use X:X:X ratio setting. If you buy two 42s, thinking the 58 can now vary the power of these it doesn't work according to the manual, but I have not tested it.
I could probably draw a Venn diagram to describe this complex-but-simple behaviour. Whatever the case, to get the best from the A900 or indeed the A700 (the 58 must be used on it to get X:X:X or X:X ratio control, the built in flash can not do it) you need either 58/58/58 or 58/48/42 as a set up.
David