More thoughts on formats

[P3D Bob Aldridge <bob.aldridge@xxxxxx>]

->Date: Wed, 4 Sep 96 12:57:26 PDT
->From: P3D John Bercovitz <bercov@xxxxxxxxxxx>
->To: photo-3d@xxxxxxxxxxxxxxx
->Subject: Re: More thoughts on formats
->Message-ID: <9609041957.AA22859@xxxxxxxxxxx>
-> 
->> Why do most 5-P format cameras lack borders between frames? 
-> 
->Basically it's because they're trying to maximize image size.
->5P at 4.75 mm per perf is 23.75 mm.  I think the mask is
->nominally 21.4 mm wide.  So there's precious little extra.
->They'd have to be very precise in their advance to give you
->a border and then there would be no room to make adjustments.
->You might get unhappy one day when, if you had had just a little 
->more image on one side, you could have gotten rid of something 
->nahstie on the other side.

I always thought that the 5-P format was chosen because you could get
two frames in between a pair without having an excessive separation...

->What would really be nice would be if the 5P cameras were
->very precise in their advances so that there wouldn't be any 
->image overlap.  Then nothing would be wasted.

The film advance IS precise, BUT the Realist has focal plane focussing.
As the film plate moves to and fro it plays havoc with the chip spacing.

->Going on to 7P, 7 perfs is 33.25 mm but the mask is only 28
->so you have tons you can throw away and still allow for uneven
->advance and for cropping.

Actually, for instance, the Belplasca has a film advance of 6 2/3
sprockets! This gives a maximum chip width of 31 2/3mm. The lens
separation is actually 63mm or thereabouts.  

-> (stuff deleted)

->In the standard 7-perf camera progression, there is one frame
->between each frame being exposed.  So 2 x 7 x 4.75 = 66.5 mm
->and that is the nominal lens spacing on a 7P camera.  66.5 is 
->much closer to the average human eye spacing than 71.25.  So
->5P cameras are slightly hyper and therefore make things look 
->slightly smaller than life size.  This also means the depth 
->cues are slightly stronger in the 5P.
-> 
->John B

Is the average human eye spacing 71.25mm? I thought it was smaller -
about 65mm, so close to the Belplasca spacing (or was that what you
meant to say?)

Bob Aldridge
Stereoscopic Society Projectionist
---
 * POW 1.3b 0007 * All those in favour of telekinesis, raise my hands.


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