The Voice Of An Artistby
SmudgeChrisComment by HarveyG: So much for the DQ.
The D90 like any AF cameras often battle when there is little or no contrast during focus.
It has no way of knowing what YOU want in focus unless you tell it.
I'm guessing your flash fired at time of shot, so there was little for it to focus on in a darkish studio, prior to the flash going off.
In the D90 manual:
P54, P59: You could have manual pre-focused the D90 on Manual Focus Mode and taken the shot.
P56: Alternatively, set it to area Mode / Single Point, switch off the "Focus Selector Lock" and choose a focus point that corresponds to your hand in the frame with the multi selector. This can be visualised through the view finder, via the "Control Panel" LCD, via the Monitor or via Live View. Switch back the focus selector lock to "L" and if on Auto Focus the D90 will use that focus point only to try focus on your hand when you take the shot (using remote or timed shot)
Try it, I battled from the getgo with these new fangled DSLR's after 30+ years of MF on 35mm SLR's but now it's a breeze and oh so useful when doing remote shots like yours.
PS: You can set up your shot and someone else is allowed to fire the trigger for you in even Basic Rules at DPC, to see that the cam has focused where you want it to.
H