FocalLengthIn35mmFormat not available for Canon?

[Martin B.]

Hi,

The FocalLengthIn35mmFormat tag works for my iPhone HEIC files, but I get nothing for my CR2 (Canon  70D) and CR3 files (an R6 and a G5Xii), even if the scale factor and the equivalent focal length appear in other tags. Is this normal? Is there a way to generate this tag rather than parsing the value of the FocalLength/FocalLength35efl tag?

exiftool -g -s -focallength "-*35*" -FocalLengthIn35mmFormat 2023-08-22_07-48-21.HEIC

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---- EXIF ----
FocalLength                     : 5.1 mm
FocalLengthIn35mmFormat         : 26 mm
FocalLengthIn35mmFormat         : 26 mm
---- Composite ----
ScaleFactor35efl                : 5.1
FocalLength35efl                : 5.1 mm (35 mm equivalent: 26.0 mm)
exiftool -g -s -focallength "-*35*" -FocalLengthIn35mmFormat 2010-05-29_17-25-02.CR2

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---- EXIF ----
FocalLength                     : 17.0 mm
---- Composite ----
ScaleFactor35efl                : 1.6
Lens35efl                       : 17.0 - 85.0 mm (35 mm equivalent: 27.5 - 137.3 mm)
FocalLength35efl                : 17.0 mm (35 mm equivalent: 27.5 mm)
exiftool -g -s -focallength "-*35*" -FocalLengthIn35mmFormat 2023-08-22_08-45-09.CR3

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---- EXIF ----
FocalLength                     : 47.0 mm
---- Composite ----
ScaleFactor35efl                : 1.0
Lens35efl                       : 24.0 - 105.0 mm (35 mm equivalent: 24.1 - 105.3 mm)
FocalLength35efl                : 47.0 mm (35 mm equivalent: 47.1 mm)
Thanks,

Martin

[Phil Harvey]

Hi Martin,

Correct, Canon doesn't write FocalLengthIn35mmFormat to CR2 files.

This is why ExifTool generates the FocalLength35efl tag.

- Phil

[Martin B.]

I see.
Is there a way to generate it on the fly with only ExifTool?

I want to generate a CSV file with the following command:
exiftool -csv -filename -caption -author -shutterspeed -aperture -iso -focallength -FocalLengthIn35mmFormat .
and I'd like to have a column with the 35 mm equivalent focal length, but nothing else (i.e. 26.0 mm, and not (35 mm equivalent: 26.0 mm) and not an empty column).

Bonus points for rounding to the nearest digit (no decimals) 

Otherwise, I'll just post-process the CSV file and parse the fields.

Thanks!

[Phil Harvey]

Here you go:

exiftool -csv -filename -caption -author -shutterspeed -aperture -iso -focallength -FocalLength35efl# .

But no bonus points for rounding.

- Phil

[Martin B.]

Thanks Phil!

And now I fully realize what I should have remembered; the value of the focal length (physical or 35mm equivalent) isn't reliable unless you have the original image. In other words, cropping and upsizing is hard to distinguish from actually zooming in (without changing the distance from the subject). Only depth of field, image quality and optical distortion would vary.

This was in preparation of images for a photo contest. Now I have to explain to the reviewers that the focal length value can be interesting to know, but it isn't reliable.