science

Lens mount

Lens mount is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lens mount rather than just read about it. In short: A lens mount is an interface – mechanical and often also electrical – between a photographic camera body and a lens. It is a feature of camera systems where the body allows interchangeable lenses, most usually the rangefinder camera, single lens reflex type, single lens mirrorless camera, or any movie camera of 16 mm or higher gauge.

Key takeaways

Lens mount belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lens mount to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lens mount from memory before moving on to harder problems.

Reference excerpt

A lens mount is an interface – mechanical and often also electrical – between a photographic camera body and a lens. It is a feature of camera systems where the body allows interchangeable lenses, most usually the rangefinder camera, single lens reflex type, single lens mirrorless camera, or any movie camera of 16 mm or higher gauge. Lens mounts are also used to connect optical components in instrumentation that may not involve a camera, such as the modular components used in optical laboratory prototyping which join via C-mount or T-mount elements.

Mount types A lens mount may be a screw-threaded type, a bayonet-type, or a breech-lock (friction lock) type. Modern still camera lens mounts are of the bayonet type, because the bayonet mechanism precisely aligns mechanical and electrical features between lens and body. Screw-threaded mounts are fragile and do not align the lens in a reliable rotational position, yet types such as the C-mount interface are still widely in use for other applications like video cameras and optical instrumentation. Bayonet mounts generally have a number of tabs (usually three or four) around the base of the lens, which fit into appropriately sized recesses in the lens mounting plate on the front of the camera. The tabs are often "keyed" in some way to ensure that the lens is inserted in only one orientation, often by making one tab a different size. Once inserted the lens is fastened by turning it a small amount, either clockwise or counterclockwise, depending on the mount. It is then locked in place by a spring-loaded pin, which can be operated to remove the lens by rotating it in the opposite direction. Lens mounts of competing manufacturers (Sony, Nikon, Canon, Contax/Yashica, Pentax, etc.) are almost always incompatible. In addition to the mechanical and electrical interface variations, the flange focal distance from the lens mount to the film or sensor can also be different, along with differing throat sizes. Many allege that these incompatibilities are due to the desire of manufacturers to "lock in" consumers to their brand. In movie cameras, the two most popular mounts in current usage on professional digital cinematography cameras are Arri's PL-mount and Panavision's PV-mount. The PL-Mount is used both on Arri and RED digital cinematography cameras, which as of 2012 are the most used cameras for films shot in digital. The Panavision mounts are exclusively used with Panavision lenses, and thus are only available on Panaflex cameras or third-party cameras "Panavised" by a Panavision rental house, whereas the PL-mount style is favored with most other cameras and cine lens manufacturers. Both of these mounts are held in place with locating pins and friction locking rings. Other mounts which are now largely historical or a minority in relation to current practices are listed below.

List of lens mounts

For small camera modules, used in e.g. CCTV systems and machine vision, a range of metric thread mounts exists. The smallest ones can be found also in e.g. cellphones and endoscopes. The most common by far is the M12x0.5, followed by M8x0.5 and M10x0.5.

M4.2x0.2 (1/7" sensors) M4.6x0.25 (1/5", 2.4mm, 3.8mm sensors, industrial endoscopes) M5x0.35 (1/6", 1/5" sensors) M5.5x0.35 (1.7", 1/5.8", 1/5", 1/4" sensors) M6x0.35 (1/4", 5.2mm, 4.85mm sensors) M6.4x0.25 (1/3" sensors) M7x0.35 (1.8", 1.7", 1/6", 1/5", 1/4", 1/3.6", 1/3.2", 1/2.7", 4.85mm sensors) M8x0.35 (1/4", 1/3" sensors) M8x0.5 (1/5", 1/4", 1/3" sensors; sometimes occurs in diode laser modules) M9x0.5 (1/2.7", 1/3", 1/3.2" sensors; also commonly encountered in diode laser modules) M10x0.5 (1/4", 1/3" sensors) M12x0.5 (the S-mount, listed in the table) M22x0.5 (1/1.2" sensors)

Focusing lens mount The axial adjustment range for focusing Ultra wide angle lenses and some Wide-angle lenses in large format cameras is usually very small. So some manufacturers (e.g. Linhof) offered special focusing lens mounts, so-called wide-angle focusing accessories for their cameras. With such a device, the lens could be focused precisely without moving the entire front standard.

Secondary lens mount

Secondary lens refers to a multi-element lens mounted either in front of a camera's primary lens, or in between the camera body and the primary lens. (D)SLR camera & interchangeable-lens manufacturers offer lens accessories like extension tubes and secondary lenses like teleconverters, which mount in between the camera body and the primary lens, both using and providing a primary lens mount. Various lensmakers also offer optical accessories that mount in front of the lens; these may include wide-angle, telephoto, fisheye, and close-up or macro adapters. Canon PowerShot A and Canon PowerShot G cameras have a built-in or non-interchangeable primary (zoom) lens, and Canon has "conversion tube" accessories available for some Canon PowerShot camera models which provide either a 52mm or 58mm "accessory/filter" screw thread. Canon's close-up, wide- (WC-DC), and tele-conversion (TC-DC) lenses have 2, 3, and 4-element lenses respectively, so they are multi-element lenses and not diopter "filters".

Lens mount adapters

Lens mount adapters are designed to attach a lens to a camera body with non-matching mounts. Generally, a lens can be easily adapted to a camera body with a smaller flange focal distance by simply adding space between the camera and the lens. When attempting to adapt a lens to a camera body with a larger flange focal distance, the adapter must include a secondary lens in order to compensate. This has the side effect of decreasing the amount of light that reaches the sensor, as well as adding a crop factor to the lens. Without the secondary lens, these adapters will function as an extension tube and will not be able to focus to infinity. In addition, active lens adapters will include electronic connections, enabling communication between the lens and the camera.

See also ISO metric screw thread Lens board

Notes ^ A: The authoritative normative source for 4/3 standards information is Four-Thirds.Org and not 3rd-party reviews. 4/3's published facts:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Lens mount

Start with the simplest possible case. Write down what Lens mount claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lens mount before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lens mount ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lens mount

In research: Lens mount appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lens mount in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lens mount is common in secondary-school and first-year university syllabi. It links to neighbouring topics Lens mounts, so understanding it makes those chapters shorter.
In everyday life: Look for Lens mount outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Lens mount in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lens mount means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lens mount out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lens mount in simple terms?

Why does Lens mount matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lens mount?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lens mount.