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Thread: Do serious movie cameras have continuously variable diaphragms?

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    can't remember Tannin's Avatar
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    Do serious movie cameras have continuously variable diaphragms?

    Just a random question only for the sake of curiosity ....

    Sometimes you will see a live telecast - football say - where part-way through a shot the cameraman changes aperture - when the ball enters the shade of a grandstand, for example. But you don't see this too often, presumably cameraman and director conspire to make changes while the particular camera is not live to air.

    But what about the movies? Let's say you have a shot that starts with the distant horizon (very bright day) and pans around to some figures in the middle distance who are in shade, then zooms in to start the conversation between them. (All in one shot.) You often see this general sort of thing. Obviously, the correct exposure is different at the start of the shot and at the end of it. If you shot that with an ordinary camera, you'd have obvious "steps" where the cameraman stopped down from (say) f/11 to f/10 and these would be quite visible. Given that I've never noticed this, I suppose that serious movie cameras have the ability to stop down steplessly and smoothly over any desired number of frames.

    Does some kind soul know for sure?

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    A royal pain in the bum! arthurking83's Avatar
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    I have absolutely no idea on how they operate, but I've had some insight into how the production of the 'movie' works(in most of my limited experience, they are commercials anyhow!).

    The lighting arrangements are well thought out way before any 'film has been exposed'.

    That is, if they know the scene exposure values are going to be so wildly variable, the lowest common denominator is used to produced a consistent exposure.

    Massive lighting arrangements are put in place to correct for the darker areas.
    The power arrangements are such that they have massive generator trucks pumping out massive doses of kilowatts mainly for the lights, but also for other uses as well.. PC's, coffee machines.. etc
    I remember stepping on one cable accidentally, and the cable was as thick as the average males wrist!

    In my previous employment as a courier, one of our regular job tasks was of deliveries of vital equipment to various production sets. Commercials(mainly), but the last one I vividly remember was the movie set of the WWII production made in and around Melbourne(I think a Spielberg movie??).

    Stupidest thing I 'never' did was hang about on set as they went about their business of making this movie. The set was located at the old train works depot in Newport, and it was stepping back in time into the 40's. Everyone was dressed in 40's garb, lots of 40's cars, trucks and so forth(I had to deliver a particular type of camera dolly), and one of my old work colleagues was working there as a gofer person. He was the bloke I was supposed to deliver this dolly too, and we got chatting, and he offered to allow me to hang about as they went about their business. It was late, and I was tired, but I never thought to use the opportunity to try to get a few photos of the set .. or at least ask.

    Anyhow .. way OT.. but how they do it(varying exposure values) with the more common consumer type digital video cameras is also beyond me.

    The problem with allowing auto variable aperture is one of DOF. Great if you want a deep DOF, but seriously limiting if the required DOF is a thin one(and of course vice versa).
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  3. #3
    can't remember
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    No, no, wander off into the broader topic by all means! Very interesting stuff!

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    I am older than I look. peterb666's Avatar
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    Both my cine camera (very early 1980s) and first video camera around 1990 did. My second video camera, I don't know as I only bought it to transfer tape to DVD.

    However bear in mind that maximum depth of field was never an issue for small format cine (Super 8) and the Video 8 formats that I had. With Super 8, minimum depth of field was OK with a f/1.2 lens and I think the Video 8 camera wasn't far behind that. Certainly for fade in and fade out in cine film there was no way other than by a continiously variable aperture. Video you can achieve electronically.

    With old camera lenses, you generally had continiously variable apertures too but with either full-stop or half-stop indents. It wasn't a hard job in most lenses to remove the small ball bearing that provided the mechanism if you wanted to eliminate the indents and to make the change in aperture smoother.
    Cheers

    PeterB666


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    can't remember
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    Thankyou Peter! I hadn't thought of the fade-out thing. Just assumed it was added later in the studio, I guess, which wasn't so bright of me.

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