No worries, glad to help....
[Trey Gregory] "Is the 'back focus' something you need to check once before you start shooting, or do you need to check it any time you change out the lens you are using?"
Once should be enough. I used to check it pretty frequently, only to find that it had never drifted out of backfocus at all, even with zillions of lens changes (and occasionally taking the body off, although not often). After a while I began to realize that the backfocus was never drifting at all, so I became more lax about checking it. Now, I check it maybe once a month. Once I got it right on the money, it has never needed adjustment.
[Trey Gregory] "Is it difficult to set this using the stock canon viewfinder in the field?"
It's not difficult... but rather darn near impossible. Your stock viewfinder will be more or less useless for backfocus adjustment. Set up a test chart in a good controlled environment, focus
precisely via distance and the witness marks on the lens, then adjust the backfocus using (if possible) a 1080 monitor... and preferably with HD-SDI or at minimum component out of the camera. If you don't have a Seimen's chart shoot me an email off list and I will send you a file that you can print out and use.
On another note, you will also find the viewfinder to be only slightly more useful for focusing. With medium-to-longer lenses (say 50mm or longer) if you shoot wide open your DoF is going to be super shallow... I've had it as shallow as one inch at close distances, so focus is going to be critical. That viewfinder (like most) is so low-res that it is extremely poor for eyeball focusing. The magnification and peaking features help some, but the best focusing is going to come from the old fashioned "Hollywood" way... a tape measure. On the left side ("port side") of the Mini35 you will see a white line and a silver knob. The white line is the "film plane" (well, it would be that if there were film), and the knob is a hook for the tape measure. Be sure you measure from the subject to the FILM PLANE, not to the front of the lens. When my subject is a human actor (the case most of the time), I measure from the film plane to their eyeballs. If eyes are sharp, then everything else is ok... but if some other parts of a scene are razor sharp yet eyeballs look soft, the whole thing looks soft.
Because tape measures are sometimes clunky to use, I also carry with me a Stanley "Fat Max" laser tape ('bout 100 bucks at Home Depot, Lowes, etc.). I use that for the majority of my focusing... I just hold it at the film plane and hit the subject with it (if the subject is an actor, though, I tell them to close their eyes).
As before, you will thank yourself if you get the weight distribution right... although I've never tried to use the P+S with another set of rails, since the Mini35 has standard 15mm/60mm rods built right into it.
I've never used that follow focus... as long as it doesn't have any slop in the gearbox, it should be ok (even widly expensive Arris still have about 1° backlash).
Hope that helps....
T2
__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com
