What is ‘focus breathing’ and how does it affect your images?

 

 

Have you ever witnessed slight changes in focal length as you bring your subject into focus? Whether or not you knew what to call the phenomenon, you've likely experienced it many times before. 

This interesting optical phenomenon is known as 'focus breathing' and in the video below, Matt Granger, formerly known as ThatNikonGuy, offers a brief tutorial.

Granger explains the phenomenon and looks at just how dramatic it can be across the ‘Nikon Holy Trinity’: 14–24mm f/2.8, 24–70mm f/2.8 & 70–200mm f/2.8. Granger even tossed in the 85mm f/1.4, to see how much difference a fixed focal length lens would make.

In my own experience, there is no real correlation between the degree of focus breathing and whether I'm using prime and zoom lenses. That is, zoom lenses don’t seem to be affected by this any more dramatically than primes. 

Unless you’re looking for absolute precision, focus breathing isn’t something that's likely to affect how you shoot on a day-to-day basis. So you can pretty much keep shooting as you are, but now you'll have an explanation ready when another photographer asks you why his lens's focal length appears to change as he dials in focus.

(via ThatNikonGuy)