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Lens

Techniques > Glossary > Lens

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This is the eye of the camera and is used to capture the image it sees onto the camera's light sensitive film, or CCD in digital camera. The size of lens is measured and indicated as a focal length. Cameras come with either a fixed lens or zoom lens with a range of focal lengths (see lens range) and on some SLR and rangefinder cameras the lens detaches so others can be attached to increase versatility. With a detachable lens camera it's often possible to buy just the body with a lens of your choice.The amount of light passing through the lens is controlled by an aperture, which is often quoted with its maximum aperture setting.Buying adviceSLRs: If you intend buying a specific lens in the future make sure that it's available in the same mount as the camera you are considering or own. Also if you're upgrading cameras, buy one with the same lens fitting or one that can be adapted to save the cost of replacing all the lenses you own.Digital and compact cameras: A fixed lens camera can often be much smaller so could be selected if you need to travel light. It's also less expensive if your budget is tight. It's better, though, to choose a camera with a zoom if you can afford to, rather than using a digital zoom or cropping the picture later. Go for one with a wider angle zoom if most of your pictures will be landscapes, interiors or family group shots.Choose a version with a longer telephoto setting if you want to shoot long distance subjects, portraits and wildlife.

Related Terms

FIXED FOCAL LENGTH LENS

(Not be confused with Fixed focus lens!) A lens that only has one focal length (as opposed to a zoom lens). A fixed focal length lens (also called 'prime lens') will often have good brightness, contrast, and be optically well-corrected. For that, it doesn't need any special glass or aspheric lens elements. Fixed focal length lenses are always superior to zoom lenses if they're made with the same optical materials and standards. They usually offer a wider maximum aperture than zoom lenses. They're often preferable for indoor shooting, but are also favourite choices as long telephoto lenses used for wildlife, sports and news photography.

Mirror lens

This is technically known as a catadioptric lens and has an unusual construction of mirrors and lens elements. As well as glass elements there are mirrors at the front and rear to fold the light as it enters the lens. Although this results in a body that's a little wider than normal, advantages are: 1. The lens is usually only half the physical length a regular lens of the same focal length would be, and 2. It's much lighter. Disadvantages are: 1. There is no adjustable aperture, so the user is forced to take all of his photos at a permanent aperture setting, usually f8, but sometimes even f11, which means you need plenty of light for taking photos; 2. Practically all mirror lenses use manual focus; 3. Highlights that are out of focus are, in some situations, shown as doughnut shapes (although some actually like this characteristic and consider it an advantage, not a disadvantage).

Retrofocus lens

Also known as a reverse or inverted telephoto, this lens design has a diverging lens element positioned in front of the aperture and a converging element positioned at the rear. This makes the distance from the rear of the lens to the focal plane longer than the lens focal length. Retrofocus design has been adopted in wide-angle lenses so the rear of the lens does not impede the movement of an SLR camera's reflex mirror.

SLR (Single-lens reflex)

An SLR or single-lens reflex camera is really designed for the enthusiast or professional photographer, or for the person who can put up with a larger camera in return for increased accuracy and greater versatility. This type of camera has through the lens viewing with a mirror behind the lens and a pentaprism to direct the light passing through the lens to the optical finder. The mirror lifts up out of the way as a photograph is taken. As you look through the lens that takes the picture, the composition can be more accurate. And in most cases you can exchange the lenses, giving you a wider scope of options. The metering and focusing systems are usually more accurate too. Despite all this creativity it's still possible to put most SLRs in a full auto point & shoot mode so anyone could use one with ease, but don't expect to fit one in a pocket! They are much bigger than that. A modern, digital version of the SLR is called a DSLR.

Apochromat (apo) lens

A special design of lens that is highly corrected to avoid chromatic aberration by bringing the three blue, red and green wavelengths to one point of focus rather than the usual blue and green of an achromatic lens. Because red is also brought to the same point of focus, you don't need to refocus when taking infrared pictures with this type of lens.

Fixed focus lens

A low-cost lens that doesn't have a focusing ring. Found in very basic cameras. The lens is set to a distance of around three meters and relies on the depth of field to bring everything from about one and a half meters to infinity. The quality is always a compromise over a lens with adjustable focusing.

Aspherical lens

A lens element that doesn't form part of a sphere. This is physically difficult to manufacture as most grinding/polishing equipment operates with a spherical action. This sort of lens is often moulded out of plastic or coated onto a glass element.

Catadioptric lens

A lens that uses reflected and refracting surfaces to form an image. More commonly known as a mirror lens.

Lens hood

Rubber or metal hood that fits on the front of a lens to shield light from hitting the edges of the lens and causing flare.

Objective lens

The second of two figures quoted on a pair of binoculars that indicates the diameter of the lens furthest away from your eye when you're looking through them. It's quoted in millimeters and the first figure is the magnification. A 10x50 pair, for example, has 10x magnification with a 50mm objective lens.

PC (Perspective control) lens

Another name for a shift lens that has a sliding front panel so the lens can be raised or lowered from its normal position to correct for verticals when shooting from high or low angles. Some also have a swing facility to control depth of field using the Scheimpflug rule.

Shift lens

A lens in a mount that can be shifted up or down to correct perspective. Also known as a PC (perspective Control) lens.

TLR Twin-lens reflex.

A camera with two lenses the upper one is the viewfinder lens that has a mirror reflex view and the bottom one is the taking lens.

Between-lens shutter

A shutter with blades that is positioned near to the aperture within a lens (also known as a leaf shutter).

Close-up lens

Sold by filter manufacturers such as Hoya and Cokin to improve the close focusing capability of a lens.

Lens coating

Transparent coated on lens elements that helps reduce reflections and flare to improve image contrast.

Macro lens

A lens that is designed to give optimum resolution at close subject distances.

Normal lens

A lens that's also called standard because it has a focal length roughly the same as the diagonal of the film format and is around the same magnification as the naked eye.

Rectilinear lens

An ultrawide-angle lens with a focal length of around 15mm that has been designed to reproduce straight lines with little distortion.

Supplementary lens

Another name for a close-up lens.

TTL (Through-the-lens) metering

A camera that takes exposure reading of the light that passes through the lens.

Wide-angle lens

A lens with a short focal length used to capture a wider angle of view.

Zoom lens

A zoom lens offers a continuously variable focal length, normally without the need to refocus. A wide-angle zoom covers a range of focal lengths that include a wide angle setting. A standard zoom goes from a slight wide angle to telephoto and a telezoom covers a range of telephoto focal lengths. Some zoom lenses are called super zooms because they cover a larger range of focal lengths from wide angle to longer telephoto.

Lens range

This is the manufacturers’ quoted focal length of the lens supplied with the camera. APS film and digital camera CCDs are smaller than conventional 35mm film so the indicated focal lengths are also smaller and should not be compared directly. For a direct comparison of APS and digital lenses look at the 35mm equivalent figures that are quoted.

PRIME LENS

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