Wanted to figure out how to set this up via expressions after seeing Blake Kathryn's animations https://twitter.com/blakekathryn/status/1322193983401910273
Ended up with something like this in the camera's 'focal' lens mm parameter:
15 *(atan2( (ch("resx")/ch("resy"))*abs(ch("tz")), 25 ))
See the notes and sources in the hip