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Leitner's Cinematography Corner, No. 6

Nov 12, 2009 12:00 PM, By D.W. Leitner

When is sharp sharp?

For projects requiring high shooting ratios in the early 1980s, you could shoot 16mm or try on for size one of those newfangled "camcorders" from Sony, Panasonic, or Bosch: Betacam, Recam, or Quartercam. (Mid-word capitalization arrived with the dot.com era a decade later.) The first two featured 1/2in. videotape cassettes, the last, 1/4in. (Ampex in the United States, original inventor of video recording, also proposed 1/4in. helical recording, but never became a player.)

Success of 1/4in. videotape, an idea ahead of its time, would await introduction of MiniDV in the late '90s, but the 1/2in. videotape camcorder took off from the starting gate. (Would you believe "camcorder" had to be coined by a reviewer? David Lachenbruch, longtime editorial director of the newsletter Television Digest, also coined "consumer electronics." Anyone know who came up with "prosumer"?)

1/2in. videotape camcorders, epitomized by Betacam, are the reason many of us first encountered the eccentricities and shortcomings of video zooms designed for electronic newsgathering. (Who came up with ENG? Or EFP, electronic field production, for that matter?)

In those days we sweated bullets over the precise mounting of our 16mm zooms from Angénieux or Carl Zeiss. 16mm was an exacting high-resolution format—see early '80s indie features blown up from Super 16 to 35mm such as Robert Young's The Ballad of Gregorio Cortez or Victor Nunez's A Flash of Green for confirmation of this—and precise lens mounting required a special device called a collimator, a technician who understood the principles of collimation (not to be taken for granted as it turned out), and deft use of metal spacers called shims (like washers used with nuts and bolts) to adjust the distance between the lens and film plane to within plus/minus 10 microns.

Collimators are like reverse telescopes. Bear with me and I’ll try to explain.

When we see stars at night, they twinkle from such unimaginable distances that their light rays reach us as parallel rays. If you were to take a simple 100mm lens, aim it at the night sky, and adjust it to infinity focus, an image of the stars would come into crisp focus exactly 100mm from the optical center of the lens. That's the definition of focal length.

In the case of a 16mm camera, the idea is to mechanically mount the 100mm lens in our example in such a way that at infinity focus, the stars are sharp. If at infinity focus the stars are not sharp, then we must disassemble the mount at the rear of the lens and insert or withdraw a few thin shims until the precise required mechanical distance between lens and film is achieved. Then, if footage markings on the focus scale of our 100mm lens have been properly inscribed, we can set focus by tape measure and rest assured that once film is developed and dailies printed and projected, the image will appear in focus.

Anyway, that's the way it worked in the heyday of 16mm. (35mm works the same way, but 16mm tolerances are far tighter and more demanding, and the toll of bad focus is steeper, since grain, more pronounced in 16mm than 35mm, is always sharp, even when the image isn’t.)

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