Hi:

This seems like a stupid question, but I don't get it. How can a camera be 1080p and have a resolution of only 900 TV lines?

Thanks, Erik

Depends on the way the sensor is designed (e.g. 3 chip or 1 chip, chips full raster or not, how the pixels on it's sensor(s) are arranged, bayer pattern processing or not etc.) plus depends on the quality of the optics/prisms/lens glass and no doubt many other things like how well the codec can preserve what it's being given from further up the chain.

"Full HD 1920x1080p" is banded around on so many cameras now but....as you've already realised, very few cameras justify this tag. It's often just "marketing tricks" aimed at unknowing consumers.

Heck, my Canon 7D is only about 600 lines in 1080p video mode even with very expensive glass on the front! At least my EX3 delivers around 1000 lines, give or take a bit!