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35mm stills camera equivalent calculation


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#1 Ray Equis

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Posted 10 June 2015 - 05:22 AM

Hi guys,

i would like to reproduce certain shots i see in movies with my stills camera. with the lens and aperture info i get from asc mag or imdb techspecs so far i have used the frame's diagonal measurent to calculate lens equivalent and depth of field equivalents. i recently bought a mamiya rzii with polaback and the while researching the net for ideas i came across the following discussion: https://www.flickr.c...57632750674921/. i get an 70x70mm (as opposed to the 69.5x56mm negative) image with the polaback. do you use the width or the diagonal to calculate lens equivalents?.
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#2 Mark Dunn

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Posted 10 June 2015 - 05:34 AM

The diagonal on square format will be a bit misleading compared with cine ARs.

Why not crop down to your preferred AR first. Presumably you already have an overlay on the focusing screen with framelines.

So 1.85 would be about 70x38mm.


Edited by Mark Dunn, 10 June 2015 - 05:37 AM.

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#3 Leon Liang

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Posted 10 June 2015 - 05:36 AM

If you want an equal horizontal field of view between your camera and, say, Super 35, use the width of the negative. So a 32mm lens on Super 35 would have a similar horizontal field of view to a 93mm lens on your Polaback.

If you want the equal vertical field of view, use the height of the negative that is used for a particular aspect ratio. So if you want to reproduce the height composition of a shot that was captured on Super 35 in 1.85:1 with a 25mm lens, but you're using a full-frame camera captures in 3:2, then use the height of 1.85:1 on Super 35, which is approximately 13mm, and the 3:2 height of a full-frame negative, which is 24mm; you would therefore need a 46mm lens on the full-frame to capture a similar vertical field of view.

I've personally never used the diagonal for anything. It seems like a compromise between the horizontal and vertical dimensions for situations where you can't decide which of the two to use.
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#4 Mark Dunn

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Posted 10 June 2015 - 05:43 AM

Assuming you have the 110 the horizontal FoV will be equivalent to about a 40 on 35mm. The 90, about a 30.


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#5 Ray Equis

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Posted 10 June 2015 - 06:27 AM

thanks guys,

ok i understood the cropping thing. now what about the depth of field?. leaving the CoC aside, would you say it relates more to the width, heigth or diagonal of the image?.
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#6 Mark Dunn

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Posted 10 June 2015 - 06:56 AM

It doesn't relate to any of them.

The book says that you will need to stop down a few stops to get a similar DoF to 35mm. but bear in mind that you probably won't be enlarging your stills to cinema size so your apparent DoF will be greater.

IIRC stills DoF usually assumes a 10x8 print viewed from a couple of feet.


Edited by Mark Dunn, 10 June 2015 - 06:57 AM.

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#7 Ray Equis

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Posted 10 June 2015 - 07:26 AM

Mark,

so CoC being related to enlargment and viewing distance is after all the main denominator. now forgive me this newbie question: how do you gauge the DoF experienced on cinema size while looking on a small monitor, or for that matter, on that on a 8x10?. please do not tell me its solely a matter of experience?. is the difference that pronounced you adapt the aperture for DoF for the every aspect ratio you shoot?.
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#8 Mark Dunn

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Posted 10 June 2015 - 10:13 AM

I can't answer that vis-a-vis monitors as i've never viewed one on set, I predate video assist, except to say that DoF does appear greater on a smaller print than a larger.

It wouldn't vary for different ARs on the same format, only between formats.


Edited by Mark Dunn, 10 June 2015 - 10:18 AM.

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