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figure out focal length


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#1 Chris Lange

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Posted 08 March 2011 - 08:53 PM

I did a test on an SONY EX3 (with stock zoom lens) prior to a rental of RED with 35mm lenses. How can I figure out what the equivalent focal length would be for a 35mm lens using RED at 16x9 RAW 4k? For instance, I would like to know what lens would work to achieve a similar focal length of 25mm on EX3? Any help on this will be much appreciated. It will be nice to go out on my first RED shoot. Nice to learn new things.

Thanks,
Chris
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#2 David Williams

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Posted 08 March 2011 - 09:51 PM

A 25mm focal length on S35 sized sensor is the same as on an EX3. Lenses are lenses, as long as they cover the sensor fully. You mean field of view.

The field of view of a 25mm on S35 is about 51 deg, that's about 7mm on a 1/2" sensor. Dividing by 3.5 is close enough.

Conveniently, IF you could stop down by 3.5 stops on the 1/2", you would also get the same depth of field on the S35.

So, a 7mm length at F2 on the EX3 would look pretty much like 25mm at about F6.7 on the Red. Field of view and depth of field looking much the same.
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#3 Hal Smith

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Posted 09 March 2011 - 12:11 AM

This page on Abel Cine's webpage should be helpful. It was created by Mitch Gross who works there and posts here from time to time.

Field of View Calculator
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#4 Mitch Gross

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Posted 09 March 2011 - 11:02 PM

This page on Abel Cine's webpage should be helpful. It was created by Mitch Gross who works there and posts here from time to time.

Field of View Calculator

Thanks for the shoutout, Hal. Actually it was created by Andy Shipsides here at Abel after I did the Sensor Comparison Chart. We each consulted with one another on how our projects should function and what they should show. Andy's far more computer savvy than I and was much better qualified to create the Comparator tool. I'd been saying for years that we needed something like this but didn't know how to do it, so I finally did the chart. Once Andy set his mind to his tool he had a beta version up in two days and the finished product within a week.
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#5 Chris Lange

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Posted 10 March 2011 - 12:54 PM

This was very helpful. Thanks a lot! In trying to replicate the field of view of the EX3 test, I will have to increase my focal length choices for RED.

Chris
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