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Focal Length Conversion


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#1 Matt Workman

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Posted 04 July 2007 - 10:56 PM

Hey,

I'm very familiar with the field of view for 35mm lenses but I've been shooting mostly on super16 and HD and I'm always scrambling to convert focal lengths.

I own a Mark VB view finder which helps me convert but not always. <_<

Can someone point me to a good focal length conversion chart? I'm mainly interested in 35mm/super16mm/HD 2/3"

Thanks,

Matt
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#2 chuck colburn

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Posted 04 July 2007 - 11:03 PM

Hey,

I'm very familiar with the field of view for 35mm lenses but I've been shooting mostly on super16 and HD and I'm always scrambling to convert focal lengths.

I own a Mark VB view finder which helps me convert but not always. <_<

Can someone point me to a good focal length conversion chart? I'm mainly interested in 35mm/super16mm/HD 2/3"

Thanks,

Matt


Hi Matt,

Panavision has one at their site. I believe it's under the tool section.

Chuck
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#3 Hal Smith

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Posted 04 July 2007 - 11:04 PM

Can someone point me to a good focal length conversion chart? I'm mainly interested in 35mm/super16mm/HD 2/3"
Matt

There's a calculator on the Panavision Nz website:

http://www.panavisio...lenseqvform.asp
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#4 Michael Nash

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Posted 05 July 2007 - 05:51 AM

Panavision's calculator is a good one because it includes all the variations of image size within each format.

But in a pinch, just remember that 16mm and 2/3" video both use focal lengths roughly half that of 35mm for a similar angle of view.
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#5 David Regan

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Posted 05 July 2007 - 09:01 PM

Could someone clarify to me what you refer to by 'focal length conversion' for different formats? I am aware that different format lenses have different properties i.e. covering power etc... but as far as focal length conversion what does that mean? My first reaction would be that a 50mm lens is a 50mm focal length on any format, as the focal length is distance from the nodal point of the lens to the focal plane. I know I must be missing something in your discussion so just wondering for clarification. Thanks.
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#6 David Mullen ASC

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Posted 05 July 2007 - 09:20 PM

Conversion factor in order to match field of view. For example, if you want to match the field of view of a 50mm lens on a 35mm movie camera, you use a 25mm lens on a 16mm camera, more or less. With 2/3" photography, it's a 2.5X factor -- for example, you'd use a 30mm lens on a 2/3" CCD video camera to match the field of view of a 75mm lens on a 35mm movie camera.
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#7 David Regan

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Posted 05 July 2007 - 09:33 PM

Ok I see, its with regard to achieving an equivalent frame, thanks David.
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#8 Michael Nash

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Posted 05 July 2007 - 09:36 PM

Could someone clarify to me what you refer to by 'focal length conversion' for different formats?


We're talking about the focal lengths needed to maintain the same angle of view between different shooting formats (usually measured horizontally), to maintain the same shot size. You're right that the focal length of a lens does not change with format, but the angle of view does. For example a 40mm lens on a 35mm camera sees about 28 degrees horizontally, but since a 16mm frame is only half the width of a 35mm frame, that same lens sees only about 14 degrees or so. So a 40mm lens gives you a medium shot on a 35mm camera, and a medium close-up on a 16mm camera (distance to subject remaining the same). To maintain the same angle of view (shot size) in the 16mm format, you need to drop down to about a 20mm lens.
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#9 David Regan

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Posted 05 July 2007 - 09:41 PM

Thanks Michael, when you refer to horizontal angle of view I assume this is an angle off a line perpendicular to the film plane?
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#10 Chris Keth

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Posted 05 July 2007 - 10:29 PM

Thanks Michael, when you refer to horizontal angle of view I assume this is an angle off a line perpendicular to the film plane?


If the lens axis (a line extending from the center of the lens) is zero. A 28 degree field of view would "see" 14 degrees horizontally on either side of the axis.

Edited by Chris Keth, 05 July 2007 - 10:30 PM.

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