Focusing through a mirror

[Sam Eilertsen]

I've noticed that when you want to focus on a reflection, you don't actually focus on the mirror, but a bit farther. Is the correct focus distance the total distance the light travels (so the distance from camera to mirror + mirror to subject)? Can anyone explain this?

Thanks,

 

[Deanan]

camera to mirror + mirror to subject.
Think of how a 3d rig where through camera and reflected camera focus to the same distance.

 

[Mike Lary]

Exactly what Deanan said.

Pulling focus between moving subjects and their reflections in mirrors can be a challenge. You have to reverse direction of the pull when switching between the two.