One of the things that I’ve wished for in Lightroom is a focal-length histogram. I’d love to be able to select a bunch of pictures and ask “which focal lengths did I use most often?” I mean, I know which lenses I use most often, but which focal lengths do I actually use?

Fortunately, it’s not too hard to do this outside of Lightroom. Just turn on XMP auto-exporting and then use the usual set of Unix tools to summarize a few thousand XML files. I used something like this:

  $ find . -name '*.xmp' | xargs grep -h 'exif:FocalLength' | 
      cut -d '>' -f2 | cut -d '/' -f1 | sort -n | uniq -c

That finds all of the .xmp files in the current directory (and subdirectories), extracts their exif:FocalLength lines, then extracts the actual focal length number, sorts them numerically, and then counts how many occurrences of each focal length it sees.

I ran this over all of the pictures that I took while on vacation, and found a couple interesting patterns. First, I usually shoot with lenses at either their short or long end; the middle of the range gets a lot less use. My most common focal lengths were

Focal Length (lens)Number of shots
70mm (24-70 or 70-200)846
400mm (100-400)409
100mm (100-400)312
200mm (70-200)304
24mm (24-70)291
85mm (85/1.8)284

A graph is (as usual) a bit more informative:

I shoot a lot of pictures in the 24-100mm range. 70mm is the most common, but the 35, 45, 55, and 65mm lines are all pretty big. It looks like I use my 24-70mm lens in the middle of its range quite a bit, while my longer lenses mostly get used at their extremes.