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There are two kinds of chromatic aberration: longitudinal and lateral. Longitudinal chromatic aberration is a variation in location of the image plane with changes in wave lengths. It produces the image point surrounded by different colors which result in a blurred image in black-and-white pictures. Lateral chromatic aberration is a variation in image size or magnification with wave length. This aberration does not appear at axial image points but toward the surrounding area, proportional to the distance from the center of the image field. Stopping down the lens has only a limited effect on these aberrations.

Spherical aberration is caused because the lens is round and the film or image sensor is flat. Light entering the edge of the lens is more severely refracted than light entering the center of the lens. This results in a blurred image, and also causes flare (non-image forming internal reflections). Stopping down the lens minimizes spherical aberration and flare, but introduces diffraction.

Astigmatism in a lens causes a point in the subject to be reproduced as a line in the image. The effect becomes worse towards the corner of the image. Stopping down the lens has very little effect.

Coma in a lens causes a circular shape in the subject to be reproduced as an oval shape in the image. Stopping down the lens has almost no effect.

Curvature of field is the inability of a lens to produce a flat image of a flat subject. The image is formed instead on a curved surface. If the center of the image is in focus, the edges are out of focus and vice versa. Stopping down the lens has a limited effect.

Distortion is the inability of a lens to capture lines as straight across the entire image area. Barrel distortion causes straight lines at the edges of the frame to bow toward the center of the image, producing a barrel shape. Pincushion distortion causes straight lines at the edges of the frame to curve in toward the lens axis. Distortion, whether barrel or pincushion type, is caused by differences in magnification; stopping down the lens has no effect at all.

The term "distortion" is also sometimes used instead of the term "aberration". In this case, other types of optical aberrations may also be meant, not necessarily geometric distortion.

Classically, light is thought of as always traveling in straight lines, but in reality, light waves tend to bend around nearby barriers, spreading out in the process. This phenomenon is known as diffraction and occurs when a light wave passes by a corner or through an opening. Diffraction plays a paramount role in limiting the resolving power of any lens.

Singlet is a lens consisting of a single element. Singlets are prone to chromatic and spherical aberrations.

Doublet is a lens design comprised of two elements grouped together. Sometimes the two elements are cemented together, and other times they are separated by an air gap. Doublets are primarily used to correct chromatic aberration, spherical aberration, and coma. An achromatic doublet consists of a positive low-index crown glass element cemented to a negative high-index flint glass element. The elements are chosen so as to cancel chromatic aberration at two well separated wavelengths; usually in the blue and red region of the spectrum. Focal length is constant at those two wavelengths and focal length shifts are virtually eliminated across the visible wavelengths. By minimizing optical aberrations, achromatic doublets produce sharper, clearer images with accurate color reproduction.

The Cooke triplet is a lens design patented in 1893 by H. Dennis Taylor, an optical manager of T. Cooke & Sons of York, and comprised of three air-spaced singlets: two biconvex (positive) elements surrounding a biconcave (negative) element in the middle. The aperture stop is just behind the central negative element. This is the simplest design that is capable of correcting all of the seven Seidel aberrations over a wide field of view. It is one of the most important lens designs in the history of photography.

A modified Cooke triplet with cemented doublets used in place of some (or all) of the singlets.

The Tessar is a lens design invented by Dr. Paul Rudolph in 1902 and patented by the Carl Zeiss company in Germany. To quote the patent document, it is "a spherical, chromatic and astigmatic corrected lens comprised of four lens elements divided into two groups by the diaphragm. One of these groups consists of two elements separated by air, the other of two cemented elements. The refractive power of the surfaces separated by air is negative, that of the cemented surface positive".

Sometimes in the literature one can find the opinion that this optical design is an improvement on the Cooke triplet, patented in 1893 by H. Dennis Taylor. Although there is a certain relationship between these two classic designs, this is not true, because Paul Rudolph took an entirely different approach. He had calculated two predecessors, the Protar and the Unar, which were completely different from the triplet. The Tessar contained parts of these two lenses, just like a child has genes from its mother and father.

The ingeniously simple design and the good performance in every aspect of lenses with moderate maximum aperture and with medium image angles made the Tessar one of the most successful camera lenses ever.

The classic double Gauss lens, patented by Alvan Graham Clark in 1888, consists of two symmetrical achromatic doublets with a positive meniscus lens on the object side and a negative meniscus lens on the image side. Derivatives of this design incorporate one or more additional elements and are the basis for many (ultra) fast standard lenses and standard macro lenses produced in the 20th century.

The Ernostar is a lens design developed by Ludwig Bertele, an employee of Ernemann-Werke, in 1923-1924. The basic Ernostar-Sonnar type is a Cooke triplet with a positive meniscus element inserted into the front airspace. The first Ernostar had a record-breaking F/2 speed for its time and was revolutionary because it allowed shooting in low light conditions at fast shutter speeds.

The Sonnar is a lens design based on the Ernostar type and patented by Ludwig Bertele, an employee of Zeiss Ikon, in 1931. The basic Ernostar-Sonnar type is a Cooke triplet with a positive meniscus element inserted into the front airspace. The main difference between Sonnar and Ernostar is not only the greater thickness of the components, but also the smaller number of air-to-glass surfaces, which improves image contrast, especially in cases where the lens does not have an anti-reflective coating.

The Biogon is a double-ended reversed-telephoto lens, consisting of a compact central positive structure with one or more large negative menisci at each end, making a roughly symmetrical arrangement. The back focal distance is so short that the lens cannot be used on SLR cameras, but it has often been used on rangefinder cameras.

The image quality of the Biogon was sensational in the 1950s, and its combination of a large field angle, perfect definition up to the corners and perfect image geometry with almost no distortion led to a real boom in wide-angle photography.

The Petzval lens is a lens design developed by Joseph Max Petzval, professor of higher mathematics, in 1840. Petzval succeeded in creating a lens free of spherical aberration, coma, astigmatism and longitudinal chromatic aberration, and its distortion and lateral chromatic aberration were insignificant. At the same time, the lens had a record speed for its time. This type of lens was proposed by Josef Petzval as a portrait lens and revolutionized the daguerreotype, which had been invented a year earlier: the Petzval lens was 16 times faster than the best lenses of the time, allowing shutter speeds to be reduced and portrait photography to be transformed from a chore into a relatively easy task.

Optically the lens consists of two achromatic doublets with an aperture stop in between; the front component is cemented, the rear one is air-spaced. The field curvature of the Petzval lens cannot be corrected, resulting in excellent sharpness only for the central part of the image and quickly decreasing towards the edges.

Dynamic range is the maximum range of tones, from darkest shadows to brightest highlights, that can be produced by a device or perceived in an image. Also called tonal range.

Resolving power is the ability of a lens, photographic emulsion or imaging sensor to distinguish fine detail. Resolving power is expressed in terms of lines per millimeter that are distinctly recorded in the final image.

Vignetting is the darkening of the corners of an image relative to the center of the image. There are three types of vignetting: optical, mechanical, and natural vignetting.

Optical vignetting is caused by the physical dimensions of a multi-element lens. Rear elements are shaded by elements in front of them, which reduces the effective lens opening for off-axis incident light. The result is a gradual decrease of the light intensity towards the image periphery. Optical vignetting is sensitive to the aperture and can be completely cured by stopping down the lens. Two or three stops are usually sufficient.

Mechanical vignetting occurs when light beams are partially blocked by external objects such as thick or stacked filters, secondary lenses, and improper lens hoods.

Natural vignetting (also known as natural illumination falloff) is not due to the blocking of light rays. The falloff is approximated by the "cosine fourth" law of illumination falloff. Wide-angle rangefinder designs are particularly prone to natural vignetting. Stopping down the lens cannot cure it.

Bright shapes or lack of contrast caused when light is scattered by the surface of the lens or reflected off the interior surfaces of the lens barrel. This is most often seen when the lens is pointed toward the sun or another bright light source. Flare can be minimized by using anti-reflection coatings, light baffles, or a lens hood.

Glowing patches of light that appear in a photograph due to lens flare.

Design with negative lens group(s) positioned in front of the diaphragm and positive lens group(s) positioned at the rear of the diaphragm. This provides a short focal length with a long back focus or lens-to-film distance, allowing for movement of the reflex mirror in SLR cameras. Sometimes called an inverted telephoto lens.

A photographic lens completely corrected for the three main optical aberrations: spherical aberration, coma, and astigmatism.

By the mid-20th century, the vast majority of lenses were close to being anastigmatic, so most manufacturers stopped including this characteristic in lens names and/or descriptions and focused on advertising other features (anti-reflection coating, for example).

Design that does not introduce significant distortion, especially ultra-wide angle lenses that preserve straight lines and do not curve them (unlike a fisheye lens, for instance).

A change in the position of the plane of optimal focus, generally due to a change in focal length when using a zoom lens, and in some lenses, with a change in aperture.

The amount of light that passes through a lens without being either absorbed by the glass or being reflected by glass/air surfaces.

When optical designers attempt to compare the performance of optical systems, a commonly used measure is the modulation transfer function (MTF).

The components of MTF are:

• RESOLUTION - an imaging system's ability to distinguish object detail. It is often expressed in terms of line-pairs per millimeter (where a line-pair is a sequence of one black line and one white line);
• CONTRAST/MODULATION - how faithfully the minimum and maximum intensity values are transferred from object plane to image plane. The lens contrast is typically defined in terms of the percentage of the object contrast that is reproduced. The sensor's ability to reproduce contrast is usually specified in terms of decibels (dB) in analog cameras and bits in digital cameras.

The MTF of a lens is a measurement of its ability to transfer contrast at a particular resolution from the object to the image. In other words, MTF is a way to incorporate resolution and contrast into a single specification.

Knowing the MTF curves of each photographic lens and camera sensor within a system allows a designer to make the appropriate selection when optimizing for a particular resolution.

Lens flare that causes loss of contrast over part or all of the image.

When light enters or exits an uncoated lens approximately 5% of the light is reflected back at each lens-air boundary due to the difference in refractive index. This reflected light causes flare and ghosting, which results in deterioration of image quality. To counter this, a vapor-deposited coating that reduces light reflection is applied to the lens surface. Early coatings consisted of a single thin film with the correct refractive index differences to cancel out reflections. Multi-layer coatings, introduced in the early 1970s, are made up of several such films.

Benefits of anti-reflection coating:

• Increases light transmission;
• Eliminates flare and ghosting;
• Maintains color consistence among all lens models.

Produces a 180° angle of view in all directions (horizontal, vertical and diagonal).

The image circle of the lens is inscribed in the image frame.

Covers the entire image frame. For this reason diagonal fisheye lenses are often called full-frame fisheyes.

Extension rings can be used singly or in combination to vary the reproduction ratio of lenses. They are mounted between the camera body and the lens. As a rule, the effect becomes stronger the shorter the focal length of the lens in use, and the longer the focal length of the extension ring.

A large-format camera with a ground-glass viewfinder at the image plane for viewing and focusing. The photographer must stick his head under a cloth hood in order to see the image projected on the ground glass. Because of their 4x5-inch (or larger) negatives, these cameras can produce extremely high-quality results. View cameras also usually support movements.