In our release notes for version 1.5 of CamCamX, we state that the Logitech QuickCam UltraVision is "just as good" as the external Apple iSight. I want to clarify what we mean by that right now.
Apple no longer sells the external FireWire iSight. I'm sure there is some stock floating around on eBay and in other stores, and if possible, our recommendation at this time is that if you are wanting a second camera for doing 2-camera shoots with CamCamX, you should definitely pick up an Apple iSight (FireWire). First of all, it is much better to have your second camera on the FW bus instead of the USB bus (we're assuming a modern Intel MacBook here). While QuickTime can open a second camera on the USB bus, we're not exactly clear on whether the second camera is always opened in high-resolution mode, or if it is reduced to a 320x240 type frame size. We'll keep you updated on that fact.
Prior to CamCamX 1.5, if you had a Logitech QuickCam UltraVision, the default processing path was conversion to RGB (the old standby) and then back to YUV for use in the video mixer. However, in version 1.5 we made specific changes to the product so that the UltraVision pixels would be just as good as the native pixels from an iSight. This is what we meant in the release notes, which were hastily written on the day of the product ship.
As far as image quality goes, it appears to us that Apple is doing some image processing on the iSight frames at the driver level. In particular, we believe they are doing a temporal based noise reduction and possibly histogram equalization on the chroma channels to make the image more vivid. Which is why the iSight simply looks better than any other webcam on the market that we've tested, both Mac and PC. And as a side note, despite the much smaller size of the camera in the MacBook, these tiny built in cameras have significantly improved image quality over the older external FireWire iSight.
In summary, when shopping for a second camera for live 2-camera webcasting, if at all possible, use a FireWire iSight, and if one of those is not available, the Logitech QuickCam UltraVision is the preferred second choice for use with CamCamX.
It is absolutely true that the USB Class Video driver included with Mac OS X and the QuickTime vdig supports the QuickCam UltraVision (you do not need MACAM or any other 3rd party driver). You do need the most up to date version of QuickTime. Support in iChat preceded support in QuickTime, as far as we can tell, so if you're running an earlier version of QuickTime (earlier than July07 7.2), it will probably work in iChat. But if you need QuickTime support, you need the July07 updates to QuickTime. At least, that's what our testing tells us. Your mileage may vary....