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Basic Training: 35mm Lens Adaptors for Video

bokeh is a Japanese word that has no English equivalent - it means "the quality of out-of-focus areas in a photograph." It's a useful word to be able to throw around at parties - photographers, news camera people and moviemakers will immediately think you're one of them if you use it properly in a sentence. (It's pronounced boke-aay or boke-uh.)

As video cameras got smaller, so did their sensors. This miniaturization was great for the people whose job it was to carry the gear, but it also opened up new avenues of camera movement and angles. Now you could put a camera on a light boom or a broom handle with a screw in it, or you could get an inexpensive steady-cam that weighed just a few pounds. One of the little-thought-of downsides is that smaller sensors mean greater depth of field.

Certainly, by far, one of the most aesthetically-appealing looks of 35mm motion picture film is the ability to have extremely shallow depth of field, isolating subjects from backgrounds and foregrounds. The zoom lenses built onto most digital video cameras simply do not have the ability to create the severe depth of field that we're used to seeing in traditional films.

When using a DSLR at wide apertures in bright light, a still photographer simply cranks up the shutter speed to get the proper amount of light hitting the sensor. With video, faster shutter speeds give a jumpy look to the final product. So how then do you reduce the amount of light hitting your sensor so you can use that big, beautiful, wide-open f-stop? Filters. Polarizers and neutral-density filters cut down the amount of light hitting your sensor without changing the colors coming in. (A polarizer makes your sky darker and reduces glare on reflective surfaces, but this is usually a good thing.) If you will be using your camera outdoors or in bright light, you'll want to have a stack of ND filters you can put in front of the lens to cut down on the light.

Some lenses work better than others. Typically, you want to use a long lens with a large f-stop. These are usually prime (non-zoom) lenses. An 85mm f/1.8 is a good choice, though the ubiquitous and relatively inexpensive 50mm f/1.8 will give good results in a pinch.

Zoom Lenses: When using a zoom lens, it's best to use one with a constant aperture. Many inexpensive zooms have smaller f-stops at the telephoto end than at the wide end, so it's not uncommon to see a lens marked 28-120mm f/3.5-5.5. This means that the widest aperture of the lens is f/3.5 at 28mm and f/5.5 at 120mm. Constant-aperture lenses, like the 80-200mm f/2.8, which is the workhorse of photojournalism, maintain the same aperture throughout the length of the zoom.

"Full Frame" Lenses: When digital SLR cameras first hit the market, they had smaller DX sensors that didn't cover the whole 35mm frame. Eventually, camera manufacturers began making less-expensive lenses specifically for small-sensor DSLRs - these lenses wouldn't work on so called "full-frame" film SLRs, because they would vignette. This is often true with 35mm video adaptors; either light falloff or the corners of the lens itself can show up in the frame.

Lenses with f-Stop Rings: Nikon made a less-expensive G series of lenses, which saved money by having no f-stop ring, controlling the f-stop electronically from the camera body. Canon followed suit with its EOS EF line. While these lenses will work, they will work only at their wide-open apertures. This may not be a problem, since the reason you're using a 35mm lens in the first place is to get the wide aperture.