Brilliant, thanks. I didn't try the slider so did not see this which is - once one knows - quite a nifty way to do this; but wasn't obvious to me.
Thanks a lot!

<t>This sounds silly, but after an hour of trying I cannot see any advanced photo or video rendering options.<br/>
I have downloaded and installed "PhotoVideoRendering2.0a.zip" and also tried "YafaryRendering 1.3.2" but in both cases the window that opens for photos shows just the space for the ...