What do lenses do

What is Lens Focal Length Focal length, usually represented in millimeters mm , is the basic description of a photographic lens.

Standard Lens FX format approx. Telephoto Lens FX format approx. Super Telephoto Lens FX format approx. More Like This More articles like this. Article Collections. Articles like this, right in your inbox.

First Name required. Last Name required. Email required. Popular Topics. More from Nikon. Close Window Share this article by email.

Your email has been sent. We like sharing articles, too! Many different kinds of lenses are manufactured for use in such devices as cameras, telescopes, microscopes and eyeglasses. Copying machines, image scanners, optical fiber transponders and cutting-edge semiconductor production equipment are other more recent devices in which the ability of lenses to diffuse or condense light is put to use.

Lenses may be divided broadly into two main types: convex and concave. Lenses that are thicker at their centers than at their edges are convex, while those that are thicker around their edges are concave. A light beam passing through a convex lens is focused by the lens on a point on the other side of the lens.

This point is called the focal point. In the case of concave lenses, which diverge rather than condense light beams, the focal point lies in front of the lens, and is the point on the axis of the incoming light from which the spread light beam through the lens appears to originate.

Concave lenses are used in eyeglasses that correct nearsightedness. Because the distance between the eye's lens and retina in nearsighted people is longer than it should be, such people are unable to make out distant objects clearly. Placing concave lenses in front of a nearsighted eye reduces the refraction of light and lengthens the focal length so that the image is formed on the retina.

Convex lenses are used in eyeglasses for correcting farsightedness, where the distance between the eye's lens and retina is too short, as a result of which the focal point lies behind the retina. Eyeglasses with convex lenses increase refraction, and accordingly reduce the focal length. Most optical devices make use of not just one lens, but of a combination of convex and concave lenses. For example, combining a single convex lens with a single concave lens enables distant objects to be seen in more detail.

This is because the light condensed by the convex lens is once more refracted into parallel light by the concave lens.

This arrangement made possible the Galilean telescope, named after its 17th century inventor, Galileo. Adding a second convex lens to this combination produces a simple telephoto lens, with the front convex and concave lens serving to magnify the image, while the rear convex lens condenses it. This is how zoom lenses work. The focused image through a single convex lens is actually very slightly distorted or blurred in a phenomenon known as lens aberration. The reason why camera and microscope lenses combine so many lens elements is to correct this aberration to obtain sharp and faithful images.

One common lens aberration is chromatic aberration. Ordinary light is a mixture of light of many different colors, i. Because the refractive index of glass to light differs according to its color or wavelength, the position in which the image is formed differs according to color, creating a blurring of colors.

This chromatic aberration can be canceled out by combining convex and concave lenses of different refractive indices. Special lenses, known as fluorite lenses, and boasting very low dispersion of light, have been developed to resolve the issue of chromatic aberration. Fluorite is actually calcium fluoride CaF 2 , crystals of which exist naturally. Towards the end of the s, Canon developed the technology for artificially creating fluorite crystals, and in the latter half of the s we achieved the first UD Ultra Low Dispersion lenses incorporating low-dispersion optical glass.

The longer the focal length, the higher the magnification. The shorter the focal length, the lower the magnification. For example, a lens with a focal length of 24mm will offer less magnification than a lens with a focal length of mm. Camera lenses come in all shapes and sizes and are designed for different shooting scenarios. However, because they have fewer lens elements, and fewer moving parts in general, they typically offer superior image quality.

This makes them suitable for portraits and product photography, or any type of photography where a soft blurry background is desired. These wide apertures also allow more light into your camera, making them ideal for shooting in low light conditions. Lenses with larger focal lengths are called telephoto lenses and offer greater magnification when shooting subjects that are far away. Macro lenses allow you to zoom in and focus on subjects at extremely close distances.

This is ideal for magnifying insects, flowers or manmade objects and capturing them in extreme detail. It can be adjusted much like the irises of the human eye, which dilate or contract depending on the available light. In general, the smaller the F-stop, the larger the aperture opening, and vice versa. Aperture also controls depth of field, which is used to separate your subject from the background.