When I used to film with a traditional videocamera, the technique was to zoom in to the subject's eye, focus and then zoom out and recompose the shot the way you want it.
I was told early on that DSLR lens' being used for video don't work that way and I have read posts on each side of the argument.
I wanted to start a discussion on focusing techniques specifically geared for us DSLR Video shooters.
One argument I've read says that only "parfocal" DSLR lens will hold their focus once you zoom out and that they are much less common these days than cheaper "varifocus" lenses which will lose their focus once you zoom out.
Philip Bloom suggests in his training videos that you use the camera's digital magnification function to enlarge the live view image on the LCD (my T2i for instance has a 5x/10x magnification button for this purpose) so you don't really zoom in for your focus.
You simply focus at whatever focal length your lens happens to be at. Philip also highly suggests using one of the Marshall external monitors with "false peaking" where whatever is in focus show up in a red outline.
I don't have an external monitor but I do have a 3x Zacutto Z-Finder which I am very happy with.
Anyways, what is YOUR favorite focusing technique and does it vary with different filming situations?
I don't have an external monitor, I would love to get that Marshall, would be great to use with my HVX also.
But I have a 2.5x Z-Finder and use the digital mag on my t2i. Find that even for a dark scene I can see the edges well enough to focus. Of course you can only do this when you are not recording unlike video cameras that allow for the focus assist when recording.
I just use the digital magnification buttons all the time; you get fast with it after a bit of practice. For follow focus, I just eyeball it but lately I'm just shooting talking heads so it's a non-issue.