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Indicates the magnification and angle-of-view of a lens. The human eye sees things roughly the same as a 43mm focal length of a lens for a 35mm camera. Anything shorter is classed as a wide-angle, while longer focal lengths are telephoto. Because of the comparatively small size of the CCD in a compact digital camera it has a standard focal length of between 6mm and 8mm while a medium-format camera is around 80mm.

Related Terms

(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.
Called 'extender', 'lens extender' or 'telephoto extender' by some manufacturers. (Not to be confused with an 'extension tube'!). A teleconverter is an accessory that fits between the camera lens and body to increase the focal length of a lens by 1.4x, 1.7x, 2x or 3x. When coupled with a 200mm lens, for instance, teleconverters would give these results: a 1.4x teleconverter gives an effective focal length of 280mm, while a 1.7x teleconverter increases this to 340mm, a 2x teleconverter to 400mm and a 3x to no less than 600mm. Teleconverters are compatible only with selected lenses, so always check with the manufacturer or retailer before buying. Although they will work with some zoom lenses, they're best used with (fast) prime lenses, since there usually is a drop in quality, and many prime lenses give a higher level of quality to start with. Besides changing the effective focal length, the effective aperture of the attached lens is increased by one or more stops as well. Autofocusing usually does not operate if the effective maximum aperture is greater than f/5.6 with the lenses/cameras from most manufacturers (in some cases greater than f/8, like on the Canon EOS 1V and EOS 3 cameras). And not all teleconverters support autofocus in the first place!
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.
An optical effect which can soften photographs and make them less sharp. As long as light travels in straight lines, this phenomenon will not occur, but as soon as it starts to bend - disperse or "diffract" - when it has to travel through a hole so small that it has to squeeze through, it will begin to interfere with the quality of the final result. Although a negligible effect in most situations, it actually increases with smaller apertures. There is a break-even point at which the disadvantage of the diffraction of the light captured is still compensated by the advantage of extra sharpness due to greater depth of field. But beyond that point the softening effect of the diffracted light is only partly compensated by the sharpness due to the greater depth of field. Finding the break-even point can help prevent any negative effects of diffraction. And as a bonus it will limit the length of the exposure or the ISO needed to take a photo with a very small aperture. The difficulty is that the effect isn't the same for different cameras and lenses. The aperture isn't the only critical factor - the size of the film or sensor recording the photo counts as well, and so does the quality and the focal length of the lens. For those who don't want to get into complicated mathematical calculations in order to find the ideal aperture, it is good to remember that the sharpest results for most lenses are found around two or three stops below their maximum aperture. Especially cheaper lenses can give very bad results at full aperture.
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).
A lens that can be adjusted from one focal length to another. Wide zooms cover a range of wide-angle focal lengths while tele zooms cover telephoto ranges and superzooms go from wide angle to a long telephoto.
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.
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.
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.
A parafocal lens, after having achieved focus at a telephoto focal length, offers the possibility of zooming back to a wide angle length, meanwhile maintaining focus on the subject. Non-parafocal lenses have to be re-focused after zooming back.
The amount of a distant scene that can be viewed using a camera lens. This varies with the focal length of the lens and film format.
A hole in the lens that adjusts in diameter, similar to the way the pupil of an eye works. This controls the amount of light reaching the film or CCD to record an image. Every different diameter opening has a number which indicates the size - it equals the focal length of the lens divided by the diameter of the aperture. These numbers are also called stops. See f/number.
The lens focal length divided by effective diameter of the aperture gives the f/number that's used to indicate the aperture value. Each full f/number, also called a stop or f-stop, halves or doubles image brightness and some lenses can also be controlled in half or third steps. The most common f/numbers are 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 and 22. They are usually preceded by an "f". The larger the f-number, the smaller the lens opening. In the aforementioned series of numbers, f/1.4 is the largest opening and f/22 the smallest. The smaller stops (larger f numbers) give the greater depth of field in a photograph, and vice versa.
Two points on the lens axis where a ray of light enters and leaves. The front point is where image distance is measured from and the rear one is where the focal length is measured from.
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.
An ultrawide-angle lens with a focal length of around 15mm that has been designed to reproduce straight lines with little distortion.
A lens with a focal length that gives a magnification greater than the naked eye.
A lens with a short focal length used to capture a wider angle of view.
A position where rays of light converge through a lens to create a sharp image. (This position is sometimes also called an "image point".) "To focus" means adjusting the distance setting on a lens to create this image point, which defines the subject sharply. With a photo camera, this is done by moving the lens physically towards or away from the film or sensor, or by moving the front of the lens towards or away from the rear part of the lens, which alters the focal length. (There are exceptions to this method: Contax, for instance, has a system where the autofocus operation actually moves the film and not the the lens.) When something is "in focus", it's sharp.
Describes how much an imaging sensor has been cropped in relation to its full-frame equivalent. It always describes how many times larger the full-frame is in relation to the cropped sensor. Take an APS-C sensor with a crop factor of 1.6, for instance. This indicates the sensor is 60% of the size of a frame of 35mm film. The crop factor is used to calculate how much of the equivalent of the full-frame field of view the cropped sensor will have with a lens. In order to calculate this, one multiplies the focal length of the lens by the crop factor. A 1.6 crop-factor, for instance, will give a 100mm lens the same field of view as a 160mm lens on a full-frame camera.