Focal Length Statistics

When thinking about buying a new prime or zoom lens for your DSLR, it is good to know some statistics of the photos you have taken in the past. In this article, we will create a histogram of the focal lengths of all pictures.

The method was tested on Linux. It might work on Mac OS X and Windows (maybe using Cygwin) as well.

First, let’s create a CSV file containing information about the camera model, lens and focal length of each picture. You can add arbitrary EXIF information in this step (see man page of exiftool).

exiftool -csv -Model -Lens -FocalLength -r <directory> > lens-stat.csv

The lines in this file look like this:

<path to image file> <a href="">puttygen </a> ,Canon EOS 550D,18.0 - 55.0 mm,36.0 mm

Optionally, you can filter this file for certain camera models and lenses. In this example, I wanted get all shots taken with my Canon EOS 550D and its 18-55 mm kit lens.

grep "Canon EOS 550D" lens-stat.csv | grep "18.0 - 55.0 mm" > lens-stat-filtered.csv

For the histogram puttygen download , we need only the last column. The unit (mm in this case) can be ignored.

awk -F'[, ]' "{print $(NF-1)}" lens-stat-filtered.csv > focal-length-stat.dat

Depending on your shell, you might have to escape the $ by writing \$.

The option -F defines the delimiter (here: comma and space), und $(NF-1) refers to the second to last column (the unit mm is the last one).

Finally, we can create the histogram:

gnuplot -p <(echo "binwidth=1; bin(x,width)=width*floor(x/width)+binwidth/2.0; set boxwidth binwidth; plot 'focal-length-stat.dat' using (bin($1,binwidth)):(1.0) smooth freq with boxes")

Again, depending on the shell, you might have to escape the $ by writing \$.

The result:

Histogram of the focal length.
Histogram of the focal length.

As it seems, I should buy both, a telezoom and a a wide angle lens 🙂

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