When you zoom in and zoom out you expect the effect to be a change in angle of view, i.e. that the subject moves closer to you or further away.
When you turn the focus ring on your lens, you expect the lens to move the focal plane back and forth to focus on different subjects in the frame.
Focus breathing is when your lens does both at the same time! As you turn the focus ring the angle of view changes as well. In other words, the closer to yourself you zoom, the shorter your lens becomes! For example the Nikon 70-200mm f/2.8 is actually a 120mm when it focuses to minimum focus distance at 200mm!
Focus breathing is for most of us not an issue, but in two cases it can cause you a headache:
- In a scene where you have two persons in the frame talking to each other and you want to focus back and forth between the two as they speak, you really don’t want to change the angle of view. It needs to be constant, otherwise the viewer gets confused at best, and a bit seasick at worst. You want that framing to be constant. For this reason, videographers absolutely do not like focus breathing.
- Macro photographers struggle with focus breathing when doing image stacking, that aims to compensate for a very shallow DOF by blending images that have been shot of the same subject with varying focus points. Here you absolutely need the framing and angle of view to be constant, otherwise the image will look very strange or at worst your post processing software wont be able to blend the images.
So should you worry about focus breathing? Not really, if you ask me. Only in the two above specific cases would I worry.
Of course it can be annoying to know that your wonderful lens has focus breathing, but now that you know what it is and in which cases it is a problem, in all other cases you can disregard focus breathing.
Thank you for reading this far! Comments and questions more than welcome!
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