FocalLengthIn35mmFilm tag definition

Started by 11august, June 10, 2017, 07:13:41 AM

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11august

June 10, 2017, 07:13:41 AM
Hello!

I have a basic question but can't find a clear answer anywhere.

It's about the specific tag "FocalLengthIn35mmFilm" as defined by the EXIF specs: it is defined as horizontal or diagonal?

Thank you!
Co-author and developper of the GEIPAN groupe image analysis software IPACO, part of the French Space Agency CNES

Phil Harvey

#1
June 10, 2017, 07:50:54 AM
35mm film is 24mm x 36mm in size.

When calculating scaling factors, I use the diagonal size.

- Phil
...where DIR is the name of a directory/folder containing the images.  On Mac/Linux/PowerShell, use single quotes (') instead of double quotes (") around arguments containing a dollar sign ($).

whugemann

#2
March 23, 2022, 05:19:53 AM
Quote from: Phil Harvey on June 10, 2017, 07:50:54 AM
When calculating scaling factors, I use the diagonal size.
I have just looked it up in Exif 2.32 - DC-008-Translation-2019-E.pdf: The official standard just says:
This tag indicates the equivalent focal length assuming a 35mm film cameras, in mm.
It does not provide any directive how to calculate this equivalent.

How does Exiftool behave in cases where this tag is present but has been calculated using, say, the horizontal field of view?

Phil Harvey

#3
March 23, 2022, 07:15:06 AM
The result will be the same as long as the picture aspect ratio is 3:2.

- Phil
...where DIR is the name of a directory/folder containing the images.  On Mac/Linux/PowerShell, use single quotes (') instead of double quotes (") around arguments containing a dollar sign ($).
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