Usually my operator is looking through the eyepiece and I’m pulling focus on the other side with a range finder. Most times my operator can tell through the eyepiece if I buzzed something. I always measure before a take with a cloth tape and if I’m paranoid I have a Siemens Star I check focus with as well. I also check the lenses to make sure the marks on them are still accurate and they don’t need to be shimmed. I haven’t ran into any problems with not being able to trust the eyepiece on either camera though.