AC90: AC90 Rack Focus

T

Todd_Sh

New member
Hi,
Apologies for the 'please teach a newbie how to use his new camera' question, but having upgraded from a basic consumer level camera, I want to not only be able to shoot better quality footage in the same style I've previously shot, I want to be able to improve my techniques to utilize the capabilities of my new camera.
So, to date, I've use the AC90 in Intelligent Auto mode, but have recently started playing with manual mode/auto focus, and manual mode/manual focus. One of the things I'd like to be able to achieve is the rack focus technique, changing focus from one subject to another in the same frame.
I know about the DOF limitations of the AC90, but was looking for some tips/ techniques to be able to best achieve this effect/style.
Thanks in advance.
Todd
 
First, you really do need to learn to operate your camera in full manual. Obviously, autofocus isn't the best idea for this type of shot (or for most any shot, really). Auto exposure and white balance can cause shifts in your image mid-shot.

With a small chip that has limited capabilities for shallow DOF, the first solution is to move the camera back and zoom in. This will increase the blur in the background. Second, open the aperture as much as you can, adding ND filtering if necessary.

You may need to experiment with the distance between your foreground focal point and your background focal point to get the effect the way you want it, but past that it's simply a matter of manually changing focus with the ring from one point to the other.
 
Alex pointed out one of the biggest challenges in rack focus with a small-chip camera - "everything's in focus". That's an overstatement, but it's hard to get a dramatic focus shift unless you're zoomed to a longer focal length - which can give you problems with positioning, particularly on small sets. You gotta be pretty far away for the effect to really pop.

The other problem is with the looseness of the focus ring - all that glass is optimized to speed up the AF, so there's very little damping and it's VERY hard to "stop" at the right spot vs. overshooting and dialing things back in. Add to this that when you're zoomed way in, the camera has to be rock-solid stable when you're touching it, or you'll see a bump.

On my DVX, I had decent luck using blue tape and marking lines, etc. But even that is hit and miss.

One solution is a remote focus controller (I use the manfrotto). Many Panasonic cameras are designed to work with these units; the external focus box has two knobs or wheels, one for close focus and one for distant; you pre-set these, and when you spin the wheel, it will not go past the two focus points. There's the added benefit of "not touching the camera", too.

These controllers can be pricey - but somewhere on this site (I think in the HMC area) there's a schematic and instructions to solder up your own. (I used that page to make a start/stop and zoom box since I own the manfrotto).

If you have a rail system going, you could try a cheap (or expensive) follow focus unit. Many of the inexpensive ones work quite well - the problem with the Panasonic is the angled rubber focus ring - focus gears for it are about $100. There are several DSLR focus rigs that use a rubber RC tire pushed against the focus ring; they're designed for SLR lenses and bodies, but might be adapted to a video cam if you're handy. A follow focus with a large marking disk can also use focus stops, which are handy when you're pulling your own focus - those small spring-clips (used to clip a stack of papers together) work great as focus stops, and they cost about a penny each.

But if you can solder, you can build a focus remote for Panasonic for under fifty bucks. And you can purchase an extension cable for using it on a crane or from a distance, too. The Manfrotto is a nice piece of gear - it has a clamp and a marking ring to repeat focus pulls.
 
Todd,

The only thing I might throw into the mix is really utilizing the focus peaking on this camera to get those smooth and accurate racks. As mentioned above using the end of your lens is key with this tiny sensored camera but having your focus peaking on (and playing around with it until your confident in understanding its response) will go such a long way.
 
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