Manual back-focus adjustment on a Sony HVR-Z7U, using a 46in. Samsung LED TV to verify the results. (Click photo to enlarge.)
Photo D.W. Leitner

I began my last column with the question, What is auto back focus?

I compared depth of field to depth of focus and described the lens factors that impact both of them. I defined correct back focus as a function of precise lens mounting, accurate to within microns of spec. And I made the case that for any given angle-of-view, the smaller the sensor, the shorter the lens focal length—and therefore the less depth of focus available at the sensor surface.

Less depth of focus always means tighter tolerances in lens mounting, which is why 1/3in. camcorders are far less forgiving of back-focus errors than 2/3in. camcorders.

Ironic, isn’t it, that smaller, consumerish camcorders require tighter tolerances in lens mounting than larger 2/3in. cameras.

So, what is auto back focus? more

The author at DuArt Film Laboratory in New York in the early 1980s, demonstrating the first lens test projector in New York.

The term “back focus� gets thrown around a lot, mostly by people who little understand it. What, then, is auto back focus?

First let’s cover some lens basics.

Lenses are two-way streets. Light can enter or exit either end. That’s what makes lens test projectors possible—the type you encounter in camera rental houses. They’re basically slide projectors, with a super-precise focus chart deposited on a glass slide. The camera lens takes the place of a projection lens.

What’s great about a lens test projector is that you can fiddle with focus, iris, or focal length (in the case of a zoom) and see with your own eyes what sort of optical gremlins reside within.

For instance, stopping down the iris, even slightly, often crispens the image by choking off residual spherical aberration—which you can easily notice as an improvement in contrast and edge sharpness. more

Sony HXR-NX5. Think Sony HVR-Z5U with slots instead of tape, for 1920×1080 capture instead of 1440×1080.

Yesterday, Jan. 6, at 7 p.m., Sony announced a new tapeless handheld, HXR-NX5, the company’s first professional camcorder to capture video to AVCHD, also known as MPEG-4 H.264.

(Note: “prosumer,� that flimsiest of marketing categories, won’t be cited in this column, ever. How can a camcorder with SMPTE 292M full-bandwidth HD-SDI output be anything but professional? Give me a break.)

Sony also announced a list price: $4,950—same as the HDV-based HVR-Z5U, which it closely resembles.

I wrote about the upcoming NXCAM line in Leitner’s Cinematography Corner #8. If you read that column, you’ll remember I was astonished that this camcorder would dock to a detachable 128GB flash memory module the size of a MiniDV videocassette and record well more than 11 hours of full 1920×1080 at AVCHD’s highest-quality bitrate, 24Mbps (VBR maximum). more

Sony SxS Pro card, 32GB of eggs in one basket, meant to be emptied sooner or later.

Since this is Cinematography Corner #13, I thought I’d share a cautionary tale bristling with misadventure and dunder-headed mistakes.

I had the privilege of touring Canon headquarters in Tokyo in November 2008, and one take-away from this visit was that solid-state flash recording is not only here to stay but positioned in product road maps to replace tape, sooner than later. And not just in consumer and low-end professional camcorders—as past months have demonstrated. more