Basic Training: Lenses - The Long and Short (page 2)

Contributing Editor Jim Stinson's book, Video; Digital Communication and Production, is just out in a second, updated edition.

Other factors being equal, wide-angle lenses have greater depth of field than telephotos, so people sometimes switch to a wider lens to make backgrounds sharper, or to a longer lens to throw them out of focus.

Neither solution will work.

The closer any lens is to its subject, the shallower the depth of field; the farther away it is, the greater the depth of field. So if you frame a closeup with a wide angle lens and decide you don't like the ugly background, you can't throw it out of focus by switching to a telephoto.

You see, to frame the same closeup with a telephoto, you have to move the lens farther from the subject, picking up more depth of field with every backward step. By the time the subject is identically framed, the more distant TP lens will deliver as much depth of field as the much closer Wide angle, and the dad-blasted background will be just as sharp as ever.

How short is your wide angle? How long is your telephoto? It depends on the size of your imaging chip. "Normal" lens perspective happens at a focal length just a bit longer than your chip, measured diagonally. Camcorder chips come in several sizes, so a lens setting that's wide angle on a small chip might be a normal setting on a larger one.

Before choosing a camcorder, consult the feature matrices on the Videomaker Web site, which list both zoom range and chip size for each model. For instance, the JVC GR-HD1 and the Sony DCR-PC350 both have about 8.5mm chips, so you know that the Sony's 4.5mm widest lens setting is a bit broader than the JVC's 5.1mm. On the other hand, the Sony model DCR-DVD201 seems to have an even wider wide end (3.2mm); but wait: its chip is only 5mm, rather than 8.5, so it's actually less wide angle than its sibling with the 8.5mm chip.

The moral? Be sure to compare apples with apples.

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