Balance between camera and flash.

[winsnick]

Hello,
I don't know whether this is in the right forum... if it isn't please can an admin move it ?
I got a speedlight sb-900 this week for my d700, great flash, especially the BL mode (automatic fill-in).
For some macro shots, I would like to underexpose the camera by 1 or 2 stops and let the flash compensate : by which I can freeze the subject better with the flash speed and faster shutter speed and darken the background.
When I put a -2ev on the camera and +2ev on the flash, I noticed an improvement in the photos but overall it is underexposed compared to the original settings.
Does anyone have an idea why ?
Thanks for your help and any tips you might have,
Nicolas.

 

[Kaouthia]

Does anyone have an idea why ?

It's just the nature of the system.

You may often have to dial 2 2/3rd extra stops into the flash if you're underexposing the scene by 2 stops.

You might want to consider signing up for a month over on Kelby Training ($25 for a month) and go watch all of Joe McNally's videos. He's got a whole bunch of different sets of training videos on there on using CLS & iTTL.