Doug Otte said:
AFAIK, they don't film anything in 16:9, unless the new HD video cameras do. Film cameras always do Academy ratio (4:3). The cinematographer's and director's monitors show the intended ratio boundaries so they can correctly frame the shot, then crop it later.
So, TNG was filmed in 4:3, but was cropped down on all sides during editing. The TATV shot above was cropped on top and bottom, but the sides (originally cropped in TNG) we retained.
Please let me know if I'm wrong about this (I often am).
You are correct that 35mm film cameras shoot with 4:3 aspect ratio (the picture is the same shape as the frame of film).
A cheap way to get widescreen is to shoot with a framing much wider than you intend for the audience to see with instuctions that the film should be matted at the top and bottom during projection to achieve a 16:9 ratio. Some eary transfers of film to VHS did not take this into account. I used to have an old VHS of a Woody Allen movie from the 70's where you could constantly see boom mics at the top of the frame and cables on the floor at the bottom. Mr. Allen is a great director and of course knew these items were in the shot, they were just never supposed to be seen. This was a case of the technician that was transfering the image to tape "projecting" it incorrectly.
The more common and more expensive technique used to get wide images on a square piece of film is to use anamorphic (panavision) lenses. The lens squeezed a wider image onto the square film frame. Then, when it is projected onto a screen, a special lens on the projector stretches the image back out to make it look normal (and wider than a 35mm film frame).
Most HD video cameras have wide (16:9) chips (the video equivalent of film) and can record the image in native 16:9, without the need of anamorphic lenses.