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RE: 35mm

Posted by David Aiken (A) on August 20, 2007 at 23:07:25

In Reply to: RE: 35mm posted by unclestu52 on August 20, 2007 at 13:27:31:

You said "Film 35 MM had some space allowed for the audio soundtrack, thus limiting the full use of the 24 mm width." Actually the width of the frame is the 36mm dimension and cutting that down to 32 mm would give you a 4:3 ratio so you're probably right there. I hadn't considered the need to allow space for the optical soundtrack and just reeled off the 35mm negative frame size from my old still photography days.

Added comment: The above paragraph is as I originally wrote it. I've since realised that 35mm film goes through the gate of a still camera at right angles to the way it travels through the gate of a movie camera so you're right, the width of the frame is 24 mm which means I have no idea what the height of the frame is. I stupidly assumed that it would be the same for a movie camera as for a still camera and it isn't. I've left the original para in to show where I was coming from.

You also said "In addition the standard TV signal has 525 lines by 720 which similarly yields a 1.37:1 ratio, although normally only 480 lines are displayed." It's what's displayed that counts and 720 pixels wide by 480 high is 3:2, not the 4:3 physical dimension ratio. You can use pixel ratios as an indication of image ratios on widescreen TVs because 1920/1080, 1366/768, and 1280/720 all basically come to 16:9, at least to roughly 2 decimal places, but that approach definitely doesn't work for standard definition screens in either NTSC (720 x 480 pixel display) or PAL (720 x 576 pixel display).

But then again, standard def displays weren't created with digital image formats in mind. If they'd bothered to think ahead we'd have been watching cinemascope movies in theatres in the 1920s and wide screen TV when TV was first introduced :-)

David Aiken

Edits: 08/21/07

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