The lens hood – an optic’s best friend

Although it is commonly regarded as an accessory, a lens hood should really be considered an integral part of the lens itself, for it unquestionably helps a lens do its job better. A lens hood (sometimes called a lens shade) serves a number of useful purposes, doesn’t wear out or require servicing, and is lightweight and inexpensive. Yet despite all these plus value many photographers never use one. Others may attach a hood occasionally when they happen to think of it, but few seem to make consistent use of this valuable lens adjunct.

The most important function of a lens hood is to control stray light – that is, light bouncing around a scene, but not contributing directly to the photographic image. For example, suppose you were taking a portrait of someone standing near a white wall, a shiny car, or some other bright surface outside the picture area. These surfaces all reflect great quantities of light. Some of the light reaches the subject you are photographing, illuminates the subject, and finds its way to the camera sensor by this perfectly acceptable route. However, much of the light output, unless it is blocked by a suitable lens hood, hits the front lens element directly and from a steep angle. It can then play havoc by bouncing around between various lens elements, degrading the image, reducing contrast, and washing out colors.

The same principle applies, although sometimes to a lesser degree, in many other situations. It is important that only light forming the image reaches the lens, not extraneous brightness from outside the picture area. Modern lens coating greatly reduces flare and internal lens reflections, but they shouldn’t be expected to do the entire job unassisted. (Of course, if you include the sun or another very bright object as part of the picture, a lens hood is powerless to protect you. Only the lens coating can.)

Because it is so important to keep non image forming light from hitting the front element, some manufacturers build in hoods as part of the lens barrel. Many long focal length lenses, including some zooms, have metal hoods that slide out for picture taking and retract for compact storage. Another way of blocking stray light is to design the barrel itself so that it extends for a distance beyond the front element. This approach is often used in shorter lenses. Also, many current lenses come with flexible, black rubber hoods that fold back out of the way when not in use. Although such hoods are readily detachable, they don’t have to be taken off when the camera or lens is stored. Therefore, they are always available when needed.

Other types of detachable hoods are made of thin, stiff metal painted black (or flocked) on the inside to further reduce reflections. They come in a variety of sizes, mostly round but some square. Like other lens accessories they may screw into the front of the barrel, clamp to the outside with a ring and setscrew, or slip on and hold with small adjustable prongs.

The most efficient and versatile light controller you can own is a compendium hood. It is pleated like a bellows and can be adjusted to any lengths within its range limits. This flexibility allows you to tailor its extension to almost any lens so that all extraneous light can be blocked off. It will also hold gelatin filters (which are less expensive than glass filters) and a variety of cutouts and masks for special effects. The compendium hood is much clumsier than a standard hood and costs a great deal more, but it is a highly effective piece of equipment.

Any lens hood is preferable to none at all. Besides minimizing light bounce and flare, a hood somewhat protects the front lens element from fingerprints, rain, blowing dust, and minor bumps. It can also protect and hold filters in place.

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