Setting up the Light Ranger during filming at the University of Oregon.
Still photographers have long enjoyed the benefits of auto-focus technology, but the technical and artistic demands of imagemaking are far more complex for cinematographers. Within each shot, directors of photography not only deal with the issue of image sharpness, but subject action, focal-plane shifts, and camera movement often all at once.While not a replacement for a good first A.C., Preston Cinema Systems’ unique Light Ranger follow-focus device has proven itself invaluable under certain conditions. This tool can automatically focus the lens through the use of an operator-controlled infrared laser and a geometric triangulation system, which determines the distance between a subject and the camera focal plane and drives a focus motor. The unit is normally mounted on its own tripod, separated from the camera by a convenient distance. An encoder head provides pan and tilt angle data so that parallax effects may be canceled out. In cases where parallax effects aren’t significant, the unit may be mounted on a conventional head.
"I’d never heard of the Light Ranger before making this film," Without Limits director of photography Conrad Hall, ASC admits, "but everybody started talking about it once we began doing some tests." Both the cinematographer and director Robert Towne decided to utilize extremely long lenses and high frame rates to shoot key portions of the film’s many running sequences. This would allow them to compress the space between central character Steve Prefontaine and his competitors, and also separate individual athletes from the field while analyzing their movements and expressions in slow motion. "There are shots done with 800mm lenses where you can see an entire 220-yard or longer run as Pre comes directly toward the camera, perfectly in focus as we tilt from his face to his shoes and back," Hall details. "Without this device, it would have been a nightmare for us to get those shots the traditional way, with follow-focus marks. Also, there are only so many times that performers can repeat action like that, so doing fewer takes was a benefit."
The inventor of the Light Ranger, Howard Preston, adds, "The need to watch the running action so closely and poetically made this a perfect application for our system."
The Light Ranger offers four modes of operation: Manual (in which the focus is controlled by a manual-control knob and the focus setting is displayed on a digital readout), Automatic (where the lens is automatically adjusted to the measured subject distance in the readout), Offset (in which the focus is still automatically adjusted but offset by a distance manually set by the operator), and Split (which allows focus "pulls" to be manually controlled by the operator). These capabilities came into play for Hall while filming a footrace between Prefontaine and rival Frank Shorter, since the cinematographer wanted the focus to smoothly transfer back and forth between the men as they jockeyed for position.
Despite the Light Ranger’s capabilities, Hall notes that the device can have operational problems under specific shooting situations, such as while trying to follow focus on someone driving a car (a situation in which the windshield or other glass surfaces may deflect the distance-measuring laser and create false readings). Also, having the camera and Light Ranger at differing elevations can affect accuracy unless such variations are accounted for.
Assessing the Light Ranger’s impact on the running sequences in Without Limits, Hall notes, "Surely it’s even more critical to have perfect focus while shooting in slow motion, as you’re expanding the action to such a great extent and emphasizing things that would not have been seen at normal camera speeds the actors’ musculature rippling, their breathing becoming more labored, their hair flowing, the sweat beading on their skin. With the Light Ranger, you have the opportunity to study all of these things as they’re happening. It becomes poetic, and makes the races interesting even though we know who’s going to win!"
Hall adds that since wrapping Without Limits, he has used the Light Ranger on several commercials, again primarily to enhance high-speed photography: "The effect of maintaining perfect sharpness is very impressive, and I much prefer this method to stopping down to an f16 to carry the focus, which also builds up the contrast."
"There are so many constraints on cinematographers who are trying to look at things in a new way," Preston remarks, "and I hope this tool removes at least one of them." He adds that continued use of the Light Ranger has led to design improvements, while noting that his current goal is reduce the size of the device and "make it as easy to use as a light meter." Currently, a qualified operator must accompany the equipment into the field.
In addition to Without Limits, the Light Ranger has recently been used on such pictures as Hard Rain (for low-light scenes, as detailed in AC Jan. 1998) and Thirteenth Warrior (for horseback sequences).