Camera Terms Glossary

CinemaTechnic Cine Camera and Lens Terms Glossary

This glossary does not attempt to be comprehensive. It simply provides definitions for some of the technical terms mentioned on this site.

Camera Terms:

Flange Focal Depth

The distance (called depth, because it is measured with a depth gage) between the reference surface of the lens mount, and the face of the camera’s aperture (gate). Ther are two values for this setting. One is the nominal depth, which is the distance at which the lens was calibrated (52.000mm for Arriflex). The second is the one used to acually set the depth from the mount to the gate. This distance is almost always shorter, because in all cameras the film curves away from the gate slightly. Also, it is desirable to have the focal plane set into the emulsion, instead of at the top surface of the film. The difference between these two settings is usually 20µm (0.02mm) for most Arriflex cameras).

This is the most critical setting on a camera, if optimum focus is to be obtained. This setting is calibrated by measuring the distance with a very sensitive and accurate gage. Each type of lens mount requires its own depth gage, and a special gage cylinder to calibrate the gage. The accuracy of the setting is specified by the manufacturer, and is usually plus/minus ten microns – 10µm (0.01mm) for older Arriflex cameras and 5µm (0.005mm) for newer ones. Panavision specifies the tightest tolerance of all at 2µm (0.0001in). Tolerances of less than 5µm are very difficult to achieve.

Ground Glass Depth

The optical distance between the reference surface of the lens mount and the front surface of the camera’s ground glass. In most reflex camera designs this distance must be exactly the same as the nominal flange focal depth setting. This ensures that exact focus will be aceived on the ground glass at the same time is is aceived on the film.

This distance cannot be directly measured, because it is an optical distance, and a right angle is present in the optical path (the spinning mirror or beam splitter in a reflex camera). The setting is checked by using a special test lens on a collimator to focus an image on the ground glass and check it’s deviation from standard.

 

Lens Terms:

Anamorphic:

In the motion picture industry this term denotes a type of lens that changes the shape of the image that is formed on the film plane. This system was brought into prominence as the Cinemascope widescreen system, which used lenses that had a horizontal angle of view that was twice the verical angle. This formed a sqeezed image on the film which was later stretched out by a matched lens on the projector. The aspect ratio on the original negative was 1.18:1 and this was stretched at a 2:1 ratio in Cinemascope to result in a widescreen aspect ratio of 2.35:1 on the projected image. Panavision began as an anamorphic projector lens manufacturer, and is now the premier supplier of anamorphic lenses for cinematography.

Aspheric:
A lens design that uses lens elements that are not sections of a sphere, but have a compound curve. These lens elemenst are very difficult and expensive to manufacture, but allow lenses using them to produce sharp images at very large apertures. Before the introduction of aspherical lenses the largest apertures on motion picture prime lenses were in the T2.2 range. The introduction of Aspherical elements in the mid 1970’s by Canon (on the K-35 prime lenses) and Zeiss (on the Super-Speed Mk. I prime lenses), along with multicoating technology, made cinematography at apertures of T1.4 or greater possible.

Collimator:
An instument that focuses light into a nearly perfect parallel beam (only a laser can achieve a truly perfect collimated beam). When a reticle is incorporated into the design, a collimator can project an image focused on infininty. Such an image can be used to check the focus calibration of lenses, and the ground glass depth on reflex cameras.

Anti-Reflective Coating:
A technology, developed by Dr. Alexander Smakula at the Carl Zeiss Co. in 1935. It reduces the amount of light that is reflected from each air-to-glass surface in a lens design. This greatly improves the contrast and sharpness of lenses. These coatings are made of super-thin layers (0.14 micron) of Magnesium Flouride, a metal that is vapor deposited on the lens elements in a vacumn.

Multi-Coating:
A newer coating technology that was developed in the mid 1970’s. Multi-Coating uses several layers of coating on a lens, each tuned to a particular wavelength of light. Multi-Coating provides the greatest efficiency in light transmission in lenses (up to 99.8%) resulting in reduced light loss and greatly improved contrast and sharpness. This is the technology that made possible zoom lenses that were as sharp as prime lenses, and also allowed maximum apertures in the T1.4 range on prime lenses. All modern motion picture lenses are multi-coated.

Planar®
A Term developed by Carl Zeiss for a symmetric lens design invented by Dr. Paul Rudolph at Carl Zeiss in 1896. The name comes from “focal plane” and refers to the flat image plane that this lens design provides. One of the most copied lens designs ever created.

Sonnar®
A Term coined by Carl Zeiss for a lens design with relatively few air to glass surfaces. Invented by Dr. Ludwig Bertele at Zeiss in 1930. The design was originally intended to provide the fastest (largest aperture) performance in 35mm photography. They were the first lenses with a f/ 1.5 stop. The name comes from the German word for sun “sonne” since this was the “brightest” lens of the time. When Dr. Alexander Smakula invented anti-reflection coating at Zeiss in 1935, it was possible to make the Planar design faster than the Sonnar. It is mostly used today for medium telephotos.

Vario-Sonnar®
A term coined by Carl Zeiss for a design similar to the Sonnar, but with a variable focal length. Used in the famous 10-100mm T3.3, T3.1 and T2.0 Vario-Sonnar lenses for 16mm cinematography, and the 11-110mm T2.2 lens for Super-16.

 

Metrology (measurment) Terms:

Micron or Micro-Metre:
One millionth of a meter (0.000001m), or one thousandth of a milimeter (0.001mm). Also referred to as a micro-metre (British spelling). The smallest commonly used unit of measure in camera service/ repair. Represented by the symbol µ as in 1µm = .001mm = 1 micron.

Electronics Terms:

Battery Memory
Battery memory is a condition that was first discovered in sattelites. The sattelites batteries had a circiut tha cut off their discharge cycle at exactly the same voltage every time, at which point the batteries were slow charged by the sattelites’ solar cell array. This caused a drop in the battery’s voltage curve during discharge, at the exact cutoff voltage. It did not a loss of capacity. Battery memory is not a problem in motion picture cameras because the batteries are never discharged to the same exact voltage every time they are used and then slow charged. Most often battery memory is suspected when the actual cause is overcharging or over-discharging.

Crystal Sync:
A system that uses the very precise frequency signal produced by a temperature-compensated quartz crystal oscillator to control the speed of a camera’s motor. The only sound-sync technology used on all professional cameras manufactured after 1972.

Fischer:
A type of high quality swiss manufactured connector used on all modern ARRI cameras. It was first used on the 16SR and 35BL-II.

LEMO:
A type of swiss manufactured connector commonly used on Aaton and Panavision cameras, as well as Preston Microforce zoom controls and some Cinematography Electronics products. Sometimes used on ARRI cameras as in the handgrip plug on the 35BL.

Tuchel:
A type of connector used on older ARRI cameras to provide an output of Pilotone signal to a Nagra tape recorder for cable-sync. This type of plug has a sleeve that screws in to lock the connector once it is plugged in. Present on ARRI cameras up to the 16SR-II. It is an obsolete system now and many 16SR owners have the Tuchel receptacle on their cameras replaced with another Fischer-11 receptacle.

Truly Obscure Stuff:

BNC (in reference to a video connector)
Bayonet Neil-Councilman plug.

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Last Update: 2/10/16

 

Optics for Motion Pictures and Digital Cinema

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