Setting camera clipping planes

[busseynova]

I've got a very simple studio scene set up, but for some reason what was taking me 2 minutes to render on one camera is taking 9 with another (slightly closer to object)

 

I'm thinking setting up clipping planes might help by cutting out unused space from the model space, I turned on 'front and back clipping' set the front to 15000 (fine, it set the back to this too) but when I try and set the back plane it just reverts both values to the length of the camera to target (about 16000).

 

Is there a system variable I'm missing?

 

Thanks,

 

Tom.

[busseynova]

Bump. Anyone? Does my question make any sense?

 

These long render times are killing me. And so will my boss if I can't hurry up.