Hi Dave,
There are two base settings on the 550 video mode, auto and manual exposure.
Auto does as it says and controls aperture,ISO and shutter speed, whereas the manual mode does allow full control over shutter speed, aperture (like you say, within the lenses capacity) and ISO too, which even set to high adds reasonably low levels of noise - i think this is low light level potential is an area where these cameras do very well indeed.
As it was a quick shoot i actually let it run in auto for this film, you can see in particulary how the shutter speed gets stepped up as on the pull focus shot between the wasp and the frit. You wouldnt see that on manual.
All focusing is done manually, it's a little tricky to get the hang of particularly if you're pulling focus in shot, you need to have a good idea of start point, end point and also make the movement ultra smooth as not to knock the camera too much. Practise makes perfect!
From the sounds of it the 550 would probably overcome the issues you're having with the 500.
I know for a fact that 550D's and 7D's are being using in broadcast programmes now, including some wildlife docs!
and then the background or foreground is in focus as far as you set the apature?
It's all to do with depth of field (DOF). With a very small apature you will find that nearly everything will be in focus - deep DOF.As you open up the apeture the the amount in focus gradually reduces - shallow DOF. You can then use your focus ring to select that distance away from the camera that is in clear focus. It's exactly the same principle with stills.
Good luck with the films, post some up!!
