ExifTool Forum

General => Metadata => Topic started by: 11august on June 10, 2017, 07:13:41 AM

Title: FocalLengthIn35mmFilm tag definition
Post by: 11august on 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!
Title: Re: FocalLengthIn35mmFilm tag definition
Post by: Phil Harvey on 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
Title: Re: FocalLengthIn35mmFilm tag definition
Post by: whugemann on 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?
Title: Re: FocalLengthIn35mmFilm tag definition
Post by: Phil Harvey on March 23, 2022, 07:15:06 AM
The result will be the same as long as the picture aspect ratio is 3:2.

- Phil