Is a follow focus system beneficial to photographers in low light or other situations? Almost all professional filmmakers use a similar system to manually focus lenses, but I am not aware of professional photographers that use it.
I find manual focus to be beneficial in many situations, such as low light, or even in instances where I am anticipating action very near to the lens against a distant background.
Overall I am looking for reasoning for and against this for photography.
"Real" follow-focus (he said, using the "no true Scotsman" fallacy) involves a separate focus puller in addition to the camera operator (whose job is primarily framing/composition). With a single operator (photographer), it's hard to manageboth the framing/composition and keeping an eye on the lens's focus scale. That, in itself, poses a bit of a practicality issue, since the working space is kind of cramped with a typical stills camera.
Yes, we did do something of the sort in the manual-focus days (with the photographer trying to maintain focus and framing at the same time, which required a bit of practice to develop the muscle memory required for each lens), but continuous autofocus has largely made this a solved problem in most instances. You can still do it, but it petty much requires either a replacement focusing screen or a small enough aperture to let DoF take care of minor discrepancies. A more standard approach with stills (especially in areas like runway fashion) is to prefocus the camera and wait for the model to hit the mark, so to speak.
What you will often see, though, is heavy use of focus memory in lenses that provide it (especially among sports photographers). Higher-end long lenses often provide a memory function that will allow you to preset focus points for quick recall when needed (so if you are shooting, say, a baseball game, you can have first base in memory and catch the play at first without having to wait for autofocus to home in on something). There are outboard systems available (usually at horrendous prices) that can add similar functionality to just about any lens -- they're designed for use in the SLR cine world, and while they're cheaper than high-end cine/video equipment, "cheaper" is definitely a relative term.
I think the only practical application of a follow focus system in stills photography would be in macro photography, where tiny adjustments of the focus ring are required to focus on different components of the scene. However in most cases the camera's focusing ring is sufficient as there is not the same need to prevent vibration of the camera that there is in video, and nor does it matter if your hand enters the frame of view temporarily while focusing.
I can't think of any other advantage to this technique in still photography, but the disadvantages are numerous; expensive, slow to focus, lack of AF, and it adds to the bulk of the camera and lens.
Follow focus is almost mandatory in DSLR video, especially as most DSLR do not do very sophisticated autofocus. There are now many kits that can be added to your DSLR to allow cinema like focus effects with something like a 5D. Folks like Red Rock Micro make these.
Also, check out Vincent LaForte's blog with nice video's of gear in action.
