Glossary

Achromatic lens

An achromatic lens, or achromat, is a lens that is corrected to reduce the effects of chromatic aberration and spherical aberration.

Additive colour

Additive colour is based on the mixing of light of different colours. By mixing three light sources with the primary colours red, green and blue, any other colour can be created. The starting point is black (no light) and subsequently coloured light is added (hence the name “additive”) and mixed. A balanced mix of the three primary colours leads to white. Early colour photography processes, like Autochrome Lumière, used the screen process to implement additive colour.

Albumen negative

The albumen photography process was introduced in 1847 by Claude Félix Abel Niépce de Saint-Victor. Albumen glass negatives had a greater resolution and were sharper than the later introduced and popular collodion negatives. It was a dry plate process and negatives could be prepared long before use and could also be developed later. The downside was that exposure times were very long, sometimes more than ten minutes. The albumen negative process was popular in France between 1847 and 1860 and used by photographers such as Claude-Marie Ferrier and Jules Couppier to create exclusive glass stereoviews.

Albumen print

The album print was introduced by Louis-Désiré Blanquart-Évrard in 1850. Albumen print was the first widely applied process for printing images on paper or glass. It became the leading printing process from 1850 to 1900. The brown toned albumen prints provided a high resolution and were capable of reproducing the fine details that were captured on an albumen or collodion negative.

Ambrotype

Ambrotype (sometimes called amphitype) was a variation of the collodion process. The appearance of a collodion glass negative as positive was first noticed by Louis-Désiré Blanquart-Évrard in 1850. The process was popularised by James Ambrose Cutting after whom the process was named. Ambrotypes were more affordable than daguerreotypes. The ambrotype direct positive process was popular between 1852 and 1870.

Anastigmatic lens

An anastigmatic lens, or anastigmat, was introduced in 1890 and designed to correct the aberration astigmatism. Anastigmatic lenses improve image sharpness and clarity by ensuring rays are focused uniformly across the image plane. The anastigmatic lenses of Carl Zeiss were called Protar.

Aplanat lens

This lens design was announced in 1866 by Steinheil in Germany as Aplanat and almost simultaneously in Britain by Dallmeyer, who called his lens Rapid Rectilinear. The design was very successful and the lenses were popular until the 1920s. The lens design was used in wide-angle and long-focus lenses.

Aristostigmat lens

The Aristostigmat lens is a high-quality photographic lens known for its correction of chromatic aberration, spherical aberration and astigmatism. These aberrations can affect image quality by introducing blur, color distortion and image distortion. The Aristostigmat lens design was patented in 1900.

Astigmatism

Astigmatism in optics refers to an aberration caused by the lens’s inability to focus light evenly onto a single point, resulting in images that are sharp in one direction but blurry in another. This is often due to the lens having different curvatures in perpendicular planes.

Autochrome Lumière

The autochrome photography process was introduced in 1907 by the brothers Louis and Auguste Lumière. Autochrome was the first practical and commercially applied colour photography process in history. The direct positive process was popular between 1907 and 1935.

Autochrome was based on the principles of additive colour and the screen process. By mixing three light sources with the primary colours red, green and blue, any other colour could be created. Autochrome plates were covered in microscopic red, green and blue-coloured potato starch grains. The layer of coloured starch grains acted as a colour filter on a monochrome glass plate negative. When a photograph was made, light passed through the colour filter before it reached the sensitive emulsion. After development, a positive colour image appeared.

Calotype

The calotype or talbotype photography process was introduced in 1841 by Henry Fox Talbot. It was the first applicable negative-positive process. The process created paper negatives which could be used to make multiple positive prints. Despite this advantage, the patent restrictions prevented the process from becoming as popular as daguerreotype, which could be used freely. Calotype was not often used for making stereo photos. The process was popular between 1841 and 1860.

Chain-based stereoscope

Chain-based or revolving stereoscopes are based on the 1857 patent of Alexander Beckers (1815–1905) from the United States. It is a multi-view stereoscope with stereoview holders that are attached to a rotating belt or chain. By rotating the belt, the stereoviews are positioned in front of the lenses one by one.

Chain-based stereoscope: Stéréoscope Américain à chaîne interchangeable

Chromatic aberration

Chromatic aberration, also known as color fringing, occurs when a lens is unable to bring all wavelengths of color to the same focal plane, resulting in a misalignment of colors at the edges of objects. This optical flaw causes images to have coloured edges around high-contrast areas, reducing clarity and sharpness.

Collodion

The collodion or wet plate photography process was introduced in 1839 by Frederick Scott Archer in 1851. Collodion was the first commercially successful negative process. The combination of collodion negatives and albumen prints allowed cheap reproduction of images with good quality. The process was popular between 1851 and 1885.

Collodion glass negatives offered very good sensitivity, which allowed short exposure times. The downside was that it was a cumbersome process. It required that the photographic material remained more or less wet during the sensitising, exposing and development of the plate. This was not a problem in a studio, but when photographers were shooting outdoors, they had to take their entire darkroom with them.

Daguerreotype

The daguerreotype photography process was introduced in 1839 by Louis Jacques Mandé Daguerre. The French government acquired the rights from Daguerre and presented the process in 1839 as a gift “free to the world”. Daguerreotype became the first process to be widely adopted and marked the beginning of the photography era. The initial process required long exposure times and was only suitable for still lifes. After optimisations, daguerreotype became suitable for making portraits. Daguerreotype was a direct positive process that was popular between 1839 and 1860.

Direct positive

A photography process in which the plate with the light-sensitive emulsion that has been exposed with the camera is developed directly into a visible image, without creating a negative. Direct positive processes created a unique image that could not be easily reproduced. An example of a direct positive process is daguerreotype.

Dry plate

See: gelatin silver

Ferrotype

See: tintype

Floor-standing stereoscope

Floor-standing stereoscopes are the largest stereoscopes and must be placed on the floor.

French tissue

Also called paper transparencies or tissue stereoviews. They were introduced in France in 1858. An image is printed on a thin layer of paper, followed by the addition of coloured paint to the back. A thin layer of tissue paper is added to the back to hide the colours and diffuse the light. The two layers are sandwiched between a cardboard frame. With reflective light, a French tissue looks like a normal image. When it is lit from behind, the added colours become visible. Sometimes new details are revealed in the so-called “surprise tissues”.

Gelatin silver

The gelatin silver or gelatin dry plate negative process was introduced in 1871 by Richard Leach Maddox. Gelatin silver negative plates retained their sensitivity for months and could be developed long after exposure in camera. It combined the benefits of both collodion negatives and albumen negatives, without their disadvantages. The process was popular between 1878 and 1940. Gelatin silver was also used to print positive images on glass for stereoscopes and magic lanterns. Gelatin silver positives on glass were popular from 1890 to 1940.

Guillotine shutter

A guillotine shutter in camera design is a mechanical shutter featuring two blades that slide vertically (up and down) to expose and then cover the negative plate, controlling the duration of exposure to light.

Hand-held stereoscope

The hand-held stereoscope is a compact and portable viewer. Many of these viewers are based on the closed box lenticular stereoscope design that was introduced by Brewster in 1849.

Hand-held stereoscope: Claudet stereoscope

Inter-ocular adjustment

Interocular adjustment is a feature of a stereoscope that can change the distance between the two oculars (the eyepieces with lenses) to match the inter-pupillary distance of the viewer. This will result in better image quality and reduces eyestrain.

Jumelle

Jumelle or photo-jumelle cameras were popular in the late 19th and early 20th centuries. The first camera was introduced by Jules Carpentier in c. 1892. Jumelle means “twin” or “binocular” in French. Jumelles had a narrow lens board and a wider plate holder, giving the cameras a shape that looked like a pair of binoculars. Both single-lens and stereo Jumelle cameras were manufactured.

Jumelle type camera: Stéréocycle

Lenticular stereoscope

A lenticular stereoscope is a stereoscope that uses lenses to view stereoscopic images. The benefit of lenses instead of the prisms of a refracting stereoscope is that lenses can magnify the image.

Long-focus lens

Long-focus lenses have a longer focal length and a smaller angle of view. These lenses are used to make distant objects appear magnified.

Stereoscope with long-focus lens: Stéréoscope à foyer long

Multi-view stereoscope

A multi-view stereoscope allows several stereoviews to be viewed in succession by turning a knob or crank or by moving a lever. Chain-based and tray-based viewers are examples of multi-view stereoscopes.

Negative

A photographic negative is an image, on glass or film, where the lightest areas of the photographed scene appear darkest and the darkest areas appear lightest. This inversion is used in traditional photography to create positive prints, where the image’s colors and luminance are corrected to their natural appearance.

Paper transparency

See: French tissue

Positive

A photographic positive is the final image that displays true colors and luminance as seen in reality, produced from a negative through a printing process. It represents the actual scene or subject without inversion of lights and shadows.

Prismatic stereoscope

See: refracting stereoscope

Protar lens

See: anastigmatic lens

Rapid Rectilinear lens

See: Aplanat lens

Reflecting stereoscope

A reflecting stereoscope is a stereo viewer that uses mirrors to view stereoscopic images. Stereoscopes based on mirrors are uncommon. Because of their size they are impractical compared to compact refracting and lenticular stereoscopes. The most well-known reflecting stereoscope is the original stereoscope that was presented by Charles Wheatstone in 1838.

Refracting stereoscope

A refracting or prismatic stereoscope is a stereoscope that uses prism lenses to view stereoscopic images.

Refracting stereoscope: Stéréoscope à verre prismatique

Revolving stereoscope

See: chain-based stereoscope

Rising front

The rising front camera movement allows the lens panel of a camera to move vertically (upwards) relative to the negative plane and exclude excessive foreground from the image. This feature was particularly useful in architectural photography to correct perspective distortion, enabling photographers to keep vertical lines straight while photographing tall buildings without tilting the camera upwards, thus avoiding the convergence of lines.

Camera with rising front: Stéréocycle Simplifié

Screen process

The screen process is used by early colour photography processes that were based on additive colour. The separation of three primary colours is effected by a transparent colour filter screen that is covered with a mosaic of grains or a grid of fine lines and/or dots in three primary colours.

During the exposure of a negative with a camera, the screen acts as a colour separation filter and exposes the monochrome emulsion with red, green and blue. The light first passes the colour filter before it reaches the emulsion. After the development to a positive image, the same screen acts as a colour filter to additively colour the white transmitted light in red, green or blue colours. The colour screen and the optical mixing of the human eye creates a full colour image.

The basic principles of the screen process were patented by Louis Ducos du Hauron in 1868. The principles were implemented for the first time by John Joly in 1894 and the Joly process was commercially introduced in 1895. Other colour processes that make use of the screen process are Autochrome Lumière and Jougla Omnicolore.

Septum

A partition that separates the two halves of a stereo camera, so that light from the left lens does not reach the right part of the negative (and vice-versa).

Short-focus lens

A short-focus lens has a relatively small focal length. It enables a larger angle of view to be observed at a closer distance.

Stereoscope with short-focus lenses: Stéréothèque à foyer court

Single-view stereoscope

A single-view stereoscope can handle only one stereoview at a time. The stereoviews are placed, viewed and replaced one-by-one.

Single-view stereoscope: Stéréoscope Standard

Spherical aberration

Spherical aberration occurs when light rays passing through the edges of a lens focus at different points than those passing through the center, leading to a blurred image. This optical imperfection is due to the spherical shape of lens surfaces, affecting the sharpness and clarity of the image.

Tabletop stereoscope

Tabletop stereoscopes are larger viewers that are intended to be placed on a table or desk.

Tabletop stereoscope: Stéréoscope Américain Simple Socle

Tessar lens

The Tessar lens, developed by Paul Rudolph for Carl Zeiss Jena in 1902, is a four-element lens known for its compact design and high-quality image sharpness, contrast, and color correction. It minimises aberrations effectively.

Tailboard camera

A tailboard camera is a type of large, portable field camera characterised by its foldable design for easy transport. It consists of a front standard holding the lens and a rear standard holding the ground glass, connected by a bellows. The tailboard, a hinged flat board at the camera’s base, supports the camera when extended for use. It was commonly used for landscape and architectural photography, offering precise focus and perspective control.

Tailboard camera: Chambre Noire Série III B

Talbotype

See: calotype

Tissue stereoview

See: French tissue

Tintype

Tintype or ferrotype was a variation of the collodion process and introduced by Adolphe Alexandre Martin in 1853. The tintype direct positive process was actually an early form of instant photography. The images were captured on iron sheets and could be made quickly and cheaply. The process was very popular between 1853 and 1930. Stereo tintypes were less common.

Tray-based stereoscope

A multi-view stereoscope for glass stereoviews that uses slide trays. Glass slides are placed in a wooden, metal or bakelite tray which is placed into the device. When operating the stereoscope, a glass slide is lifted or pulled out of the tray and placed in front of the lenses. The slide is then placed back, the tray is moved further on a rail and the next slide is loaded. Some designs have a mechanism to quickly jump to a specific slide in the tray. Tray-based devices are the most advanced stereoscopes and offer the best viewing comfort.

Tray-based stereoscope: Taxiphote Modèle Optique

Wet plate

See: collodion