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Why are projector apertures smaller than camera apertures?


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#1 cole t parzenn

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Posted 28 June 2014 - 04:19 PM

I've long wondered; camera apertures are pretty darn small, to begin with. Grazie.


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#2 Brian Drysdale

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Posted 28 June 2014 - 05:24 PM

Tolerances and you're less likely dirt and hairs, which sometimes can collect in the camera gate during a take being projected.


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#3 Keith Walters

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Posted 28 June 2014 - 05:57 PM

First of all, because the film is a strictly 2-D image, there is no concern about depth of field, since the only depth of field is that already recorded on the film.

 

However a smaller aperture (and consequently larger depth of field)  makes the image focus less affected by fluctuations in the distance between the film surface and the rear element of the lens.

 

In a camera there is usually an elaborate mechanism for holding each frame precisely in place during exposure, but this is out of the question for a projector, both because of the cost,  and also  because the mechanism would rapidly wear out, since the average film projector sees vastly more film footage than the average camera.

 

Also, film projectors generate a lot of heat from the projection lamp which can also distort the film. For slides you can get more expensive holders with thin glass plates that prevent this, but this is not possible for movie film.

 

Also, as Brian says, it's basically cheaper to use a lesser-quality lens, stopped down to disguise its optical deficiencies, and  use a brighter lamp to overcome the light loss.


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#4 cole t parzenn

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Posted 28 June 2014 - 06:16 PM

Tolerances and you're less likely dirt and hairs, which sometimes can collect in the camera gate during a take being projected.

 

Makes sense. Hypothetically, how likely is it that the audio track would accidentically be projected, if the projector's aperture were the same as the camera's?


 

First of all, because the film is a strictly 2-D image, there is no concern about depth of field, since the only depth of field is that already recorded on the film.

 

However a smaller aperture (and consequently larger depth of field)  makes the image focus less affected by fluctuations in the distance between the film surface and the rear element of the lens.

 

In a camera there is usually an elaborate mechanism for holding each frame precisely in place during exposure, but this is out of the question for a projector, both because of the cost,  and also  because the mechanism would rapidly wear out, since the average film projector sees vastly more film footage than the average camera.

 

Also, film projectors generate a lot of heat from the projection lamp which can also distort the film. For slides you can get more expensive holders with thin glass plates that prevent this, but this is not possible for movie film.

 

Also, as Brian says, it's basically cheaper to use a lesser-quality lens, stopped down to disguise its optical deficiencies, and  use a brighter lamp to overcome the light loss.

 

I was thinking more about the projector's aperture/gate than the lens' but thank you - that's interesting, as well.


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#5 David Mullen ASC

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Posted 28 June 2014 - 07:47 PM

Besides hairs in the gate, there are also splices to hide.


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#6 cole t parzenn

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Posted 28 June 2014 - 09:26 PM

How visible would a splice be?


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#7 Keith Walters

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Posted 28 June 2014 - 10:31 PM

I've long wondered; camera apertures are pretty darn small, to begin with

 

What sort of cameras are you talking about? On all  of the 35 and 16mm cameras I've seen, the gate is almost as big as the allowable picture area.

It's smaller for standard 1.33:1, because they mask off the soundtrack area, so you're going to get a small blank bit at the top and bottom of frame, but for full-height Super-35 (ie "Silent Gate") it's about as big as it can be.

 

The main reason they make the projector gate a little bit smaller than the actual film image  is simply that it hides jitter on the edges of the frame. A slight picture  jitter itself can be tolerated, but not if it involves the frame edge moving in and out of view.


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#8 Brian Drysdale

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Posted 29 June 2014 - 03:57 AM

How visible would a splice be?

 

Chemical spices can be pretty visible on the smaller film formats, especially 8mm. The splices used for neg cutting are narrower.

 

http://www.nfsa.gov....lossary/splices


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#9 cole t parzenn

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Posted 29 June 2014 - 10:27 AM

Thanks. So, what happens when the camera and print format are different, e.g., S35 or S16?


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#10 Gregory Irwin

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Posted 29 June 2014 - 10:28 AM

Are we talking about light levels or gates? If gates, cameras have larger gates in order to see beyond the frame lines. We call it "full aperture". We can see things about to enter frame before they do and monitor things such as microphones, boomed overhead to see their relation to the frame line. Projectors simply have the need to project the aspect ratio and thus are matted to reflect such.

With reference to gate hairs, if they appear in full aperture, they most likely are not in frame and not a problem. That's what make 2 perf so tricky. The aspect ratio is full aperture. Hairs are always in frame.



G
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#11 Brian Drysdale

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Posted 29 June 2014 - 11:24 AM

Thanks. So, what happens when the camera and print format are different, e.g., S35 or S16?

 

S35 and Super 16 are not print formats, they're for acquisition, for film projection in theatres normal 35mm prints are made from the camera negatives through a DI or in the past an optical internegative.


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#12 cole t parzenn

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Posted 29 June 2014 - 11:30 AM

But are they printed to extend beyond the projector gate?


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#13 David Mullen ASC

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Posted 29 June 2014 - 11:33 AM

If the camera format does not allow contact printing all the way through to a print that can be projected with an optical soundtrack, then there is either an optical printer step or (more likely today) a digital intermediate step to create a dupe negative that can be contact printed for release prints.

 

Greg, a hard matte in a camera gate that only allows the projection area to be exposed does not negate the ability of the operator to see beyond that area since his viewfinder receives an image split from the mirror shutter before the light reaches the gate.  The ability to see full aperture or beyond in the viewfinder is more a matter of the ground glass and how much of the projected image from the lens is allowed to reach the viewfinder optics.

 

There are some examples of features shot with camera gates with hard mattes to only expose 1.37 Academy or 1.66 or even 1.85 instead of full aperture in 4-perf 35mm. 

 

The main reason we expose more than what is projected is that projection evolved beyond showing the 1.33 silent (full) aperture of 4-perf 35mm.  But even back then at the dawn of cinema, probably projection gates were slightly smaller than camera gates due to issues like gate weave, jitter, and splices, not to mention dirt on the camera gate, that would be distracting for the audience to see along the top & bottom of the frame.  But once sound movies came along and an optical track had to be added to the side, projection gates in general were masking more and more of the 4-perf 35mm full aperture area.

 

35mm anamorphic (scope) projection used almost the full height of the print area and even this was shaved down in the early 1970's (the projector mask was shortened slightly) to hide splices better, changing the aspect ratio from 2.35 : 1 to almost 2.40 : 1.


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#14 David Mullen ASC

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Posted 29 June 2014 - 11:38 AM

It's a good question about whether a D.I. would record an image to 4-perf 35mm that was slightly oversized than the projection area.  With a 1.85 movie, sure, most movies would probably put a 1.78 area at least (if not taller) onto the piece of film so that if the projectionist slightly misframed the image vertically, the audience wouldn't see black borders creeping into the image top or bottom.

 

But for 2.40 scope movies, I don't know if a D.I. would record out to 4-perf 35mm film an image that was exactly the height of the scope projection aperture or slightly taller, the height of an anamorphic camera aperture. You'd have to talk to a D.I. company about the specs for the laser recorder.

 

It's all a bit moot now that most movies are digitally projected.


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#15 cole t parzenn

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Posted 29 June 2014 - 11:41 AM

Moot, yes - still interesting, though. Thanks, everyone!


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#16 Gregory Irwin

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Posted 29 June 2014 - 12:44 PM

 
Greg, a hard matte in a camera gate that only allows the projection area to be exposed does not negate the ability of the operator to see beyond that area since his viewfinder receives an image split from the mirror shutter before the light reaches the gate.  The ability to see full aperture or beyond in the viewfinder is more a matter of the ground glass and how much of the projected image from the lens is allowed to reach the viewfinder optics.


Very true, David. Very true.
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#17 Keith Walters

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Posted 02 July 2014 - 07:38 PM

In my experience at Panavision Australia anyway, very few customers chose to hard-mask the negative when shooting 1.85:1; they would always shoot full-frame and let the projector do the masking.

The only people who insisted on 1.85:1 masking seemed to be producers paranoid about their movies being shown on 4:3 TV, with the normally-cropped parts being used as an alternative to the black bars of letterboxing.

Which didn't do them a lot of good, because in the US at least, such films were routinely telecast with a 4:3 slice taken out of the 1.85:1 image, regardless of any contractual agreements. American TV audiences  seem to have always had a morbid fear of "Black Bars", (or maybe they just  felt that they paid good money for screen real estate that wasn't being used :rolleyes: )

Whatever, traditionally European audiences seemed far less bothered by such things.


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