Portrait Focus Question - Manual Focus Medium Format

<p>I will be shooting some portraits of the kids this weekend and I have a couple questions about the best way to focus given my intended setup. I will be using my Pentax 67 MF camera with a 165mm f/2.8 lens. I will also have the camera mounted on a tripod and will be using Provia 400X film. My idea is to use available light during the "magic hour" in the evening. I may use some reflectors for fill, but by-and-large it will be an available light shoot, so no flash. That's why I chose a 400 speed film over a slower alternative. Also, two of my kids are on the young side (2 - 4 years old) so they don't sit still too well, so I figure I'll need all the shutter speed I can get. Here's the question... Since I will be manually focusing and probably even using MLU, what is the best way to focus given the subject may move around a little bit while I'm trying to take the exposure? I'm used to continuous auto focus so I typically don't have to deal with this issue. However, given the depth of field issues associated with MF cameras, how should I set my focus and or f/stops to ensure my subjects are in focus since I will likely not be able to re-focus with them as they move around (just prior to taking the exposure)? I will have them seated so the movement will likely be minimal, but probably still enough to make a difference. My original thought was to hopefully have enough light to allow me to use at least f/8, maybe even f/11 to maximize DOF, thereby keeping their face mostly in focus in case there was movement. Thoughts?</p>

<p>You're down with the major issue--DOF. Try to keep the kids in the same(OK, make that as close as possible)plane of focus. One sitting back a foot or so from the front subject just won't cut it. If they won't cooperate, shoot one or two together. There are lots of poses, especially at ground level, that will allow this without the police line-up look--getting them on the ground actually seems to reduce squirming, too. Meter and go with the best DOF/shutter speed available. I'm guessing 1/30-1/60 will work if they're not too jumpy. It's really a matter of conditions and experimentation. Be patient and make sure they're well-fed before your shoot. These sorts of things always upped my chances of a reasonable keeper quotient. Be prepared to burn some film.</p>