Today’s Question: I noticed there is a “Focal Length 35mm” field in Lightroom Classic, but it is empty for all my photos. Is there a way to populate this field with the applicable values?
Tim’s Quick Answer: The “Focal Length 35mm” field in Lightroom Classic requires that the camera wrote the information to metadata for the photos, and you can’t edit the value in Lightroom Classic.
More Detail: The “Focal Length 35mm” EXIF metadata field is intended to contain the equivalent lens focal length based on a 35mm (full-frame) sensor. So, for example, if you were using a camera with a full-frame sensor, the “Focal Length 35mm” field would show the exact same value as the “Focal Length” field. If you were using a camera with a 1.5X cropping factor and had used a 100mm lens, the “Focal Length 35mm” field would show the effective focal length of 150mm.
However, not all cameras write this information to metadata. Based only on the photos I have in my own library, I haven’t found a single Canon camera that writes this information to metadata, while Nikon and Sony cameras (at least the models from which I have photos) do write this information. The Apple iPhone also saves this information to metadata. But this is obviously not based on any exhaustive research or photo library. It is just to illustrate that some cameras write this information to metadata and others don’t.
The “Focal Length 35mm” field, like most EXIF metadata, is not editable in Lightroom Classic. There are third-party metadata editing tools that enable you to edit EXIF, and I would assume those tools therefore enable you to edit the “Focal Length 35mm” field. However, this isn’t something I would recommend doing in general, and it is also something that would most likely not be a very efficient process in terms of automating the update for multiple photos.
