Lenses - The Long and Short

Wide-angle and telephoto lenses render images differently from the way we naturally see things. Skilled videographers can exploit these differences to create effective shots.

Many people use wide-angle lens settings only to "back away from" subjects and telephoto settings to "move closer." More experienced videographers exploit the distinct qualities of wide-angle and telephoto lens settings to determine perspective, enhance composition, control focus and background and affect movement within the frame.

So let’s review the qualities of WA and TP lenses, and then suggest some ways to exploit their abilities and work around their limitations. (Since normal range focal lengths behave, well, normally, there’s isn’t much to say about them.) For simplicity, we’ll discuss WA and TP "lenses," when we really mean different focal length settings on a single lens that can zoom from one extreme to the other.

Different Focal Lengths

As any optical engineer will vehemently insist, various focal lengths differ optically only in the angles of view they cover. Wide-angle lenses can take in up to about 90 degrees, while telephotos "see" as few as five degrees or less. In the middle range, lenses covering around 48 degrees appear "normal" because they roughly match the characteristics of human vision (Figure 1).

In fact, lenses typically show other optical differences. Wide-angle settings are usually "faster" than telephotos, meaning they can admit as much as two f-stops more light. That’s why lenses show labels like "f2 — f4," meaning that the maximum aperture is f2 at extreme wide angle but only f4 at full telephoto.

Also when WA and TP lenses are set at the same f-stop and focused at the same distance, the telephotos will deliver less depth of field (the distances that remain sharp both before and behind the subject).

However, the most dramatic differences between focal lengths are not optical but pictorial: the appearance of the image rendered by the lens. These differences include apparent spatial depth, subject size and movement.

The most dramatic contrast is in apparent depth ("apparent" because flat video images have no actual third dimension). Wide-angle settings exaggerate depth, making everything look more spacious. Telephoto lenses compress depth, squeezing foreground and background together (Figure 2).

A closely related difference is apparent size. Notice that the background figure in the WA shot (Figure 2a) looks much smaller than in the TP shot (Figure 2b) even though the two figures are the same distance apart in both setups.

The last big difference is apparent speed of movement. Because WA depth seems so great and figures shrink or grow so fast as they move forward or backward, WA movement in depth seems very fast and dramatic.

By contrast, subjects in telephoto shots can move toward the camera, and move and move and move and never seem to get anywhere, because they are covering the squeezed-
together depth of the TP perspective.

Different Traits, Different Uses

Wide-angle lenses are often selected because their larger maximum apertures make them more useful in low-light shooting situations. Sometimes, a wide-angle setting will admit enough light for a good exposure, where a slower telephoto setting would force the camcorder to increase the amount of gain (and with it, graininess and noise). Wide-angle settings are also better for moving shots because they minimize the effect of camera shake, while telephoto settings exaggerate it.

Finally, wide-angle lenses deliver dynamic action when subjects move toward or away from the camera. Fights and chases look doubly exciting because they rush through so much apparent space. Of course, you won’t get the same effect when the action moves from side to side, because lenses affect only the third ("Z axis") dimension.

Otherwise, WA and TP lenses have just about equal and opposite advantages and problems. Telephoto lenses get the nod whenever you need to bring distant subjects closer — like wildlife or sports. When you watch a shot of a baseball pitch from behind the pitcher, remember that the video camera is hundreds of feet back, on the far side of center field, and fitted with a monster telephoto lens.

By contrast, wide angles are worth gold in small rooms and other confined spaces, because you can orient the viewer with establishing shots that would be impossible with longer lenses.

In the process, WA lenses make those small rooms look bigger — sometimes much bigger. Look at infomercials for RVs, resort hotels, or cruise ships if you want to see the camera turn 8 x 10 closets into spacious suites.

On the other hand, if you want to editorialize about urban claustrophobia, just zoom into telephoto and train your camcorder down a long, straight, busy boulevard. Your TP lens will crush a mile-long string of cars, light poles, and pedestrians into 100 yards of congested, smoggy chaos.

You can use the same tricks with distance to control backgrounds. If you must shoot a subject against an unattractive background, a wide-angle lens will show it as far away and indistinct.

But suppose you want to emphasize the relationship to the background behind the subject? A reporter may do her standup outside the fence and hundreds of yards from the White House; but a long telephoto will bring the Executive Mansion close enough to loom importantly behind her.

WA and TP lenses have markedly different effects on closeups. By minimizing depth, mild TP settings often make more pleasing portraits of women. Contrariwise, moderately wide-angle settings can add some macho ruggedness to male closeups. Beware of either extreme: too much TP turns faces into blobs, while excessive WA distorts features and turns noses into toucan bills.

Composing with Focal Lengths

When you set your lens to wide angle, you’re going for depth, so create compositions that strengthen that illusion. Look for converging lines of horizontal and vertical objects such as streets and light poles. Low angles emphasize these converging lines, while dramatizing movement toward and away from the camera.

Composing with telephoto settings is more difficult, until you get the hang of arranging elements on the picture plane (a.k.a. the screen). Start by suppressing the idea that you’re looking through the lens and remind yourself that you’re looking at the flat viewfinder (working with the external LCD screen is especially useful).

Now try to imagine that you’re designing a bulletin board, pinning up various shapes in different parts of the rectangle to make an effective two-
dimensional arrangement.

Once you get good at it, you’ll find yourself treating all compositions as combinations of solids in virtual space. Don’t ask me how it works — but I suppose you could think of it as how the left and right hands can do completely different things on a piano’s keyboard to somehow play a grand, unified composition.

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

Sidebar One: Focal Length and Focus

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.

Sidebar Two: Focal Length and Chip Size

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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