Thank for your continued interest guys, it gives me hope!
Originally posted by Class A Have you checked whether you have set a positive flash exposure compensation on the Sigma EF-610 DG Super?
It should be neutral. If there is no positive flash exposure compensation set, check if you can perhaps dial in a negative one.
In any event, using a negative exposure on the V6II transmitter on the group the Sigma is assigned to, should fix your problem as well.
The idea of power settings in TTL mode is that they are relative "modifiers", equivalent to flash compensation values one would set on the flash itself or per-flash settings on the camera (for systems, like Canon's, that support this).
Yes, there's no exposure compensation set on the Sigma EF-610 DG Super. If I do dial in some negative EV (max -3.0) on the Sigma
plus have the V6II set at -5.0 EV, I can obtain an exposure that is 'averagely' exposed when using TTL; so I was under rating the difference when I said it was 3-4 stops out. If I then also add -2.0 stops EV on the K3 flash metering then I can at last achieve an underexposed image. Of course the problem here is that the K3 flash EV would also be applied to my other flash/es as well wish is less than ideal.
The problem seems to be that the V6II's starting point - the 'Pentax Auto Profile' is for a flash with a much lower guide number; the EF-610 DG Super's is 61 @ 105mm.
Note that using a custom profile only makes a change to the manually set flash output, it makes no difference when using TTL.