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Rotary disc shutter
Rotary disc shutter
Rotary disc shutter
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When the shutter is open, the film is exposed. When it closes, the next frame of film is brought into position by the claw.
Adjusting the shutter angle affects the amount of time that film is exposed to light.

A rotary disc shutter is a type of shutter. It is notably used in motion picture cameras.[1][2] Rotary shutters are semicircular discs that spin in front of the film gate, alternately allowing light from the lens to strike the film, or blocking it.

Details

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Rotary shutters are semicircular discs that spin in front of the film gate, alternately allowing light from the lens to strike the film, or blocking it. When blocking the light, the exposed portion of the film is advanced, and another, pristine frame is moved into position. The spinning disc then exposes the new frame of film. The nature of light-sensitive film requires a shutter to block the light and prevent smearing of the image as the film is advanced through the camera. Digital sensors do not require a rotary shutter, although some high-end digital cinema cameras do have them. Some rotary shutters utilize mirrors (or mirrored surfaces) so that when the shutter is in its closed position, light from the lens is redirected to a viewing system, allowing the camera operator to view, frame, and focus the image, exactly as the film sees it.

Shutter Angle

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On more advanced cameras, the open portion of the shutter can be adjusted. This shutter setting is referred to as the shutter angle. Adjusting the shutter angle controls the proportion of time that the film is exposed to light during each frame interval. The angle of the shutter forms a proportion to the time that each frame of film is exposed:

.

The primary reason that cinematographers adjust the shutter angle is to control the amount of motion blur that is recorded on each successive frame of film. A tight shutter angle will constrict motion blur. A wide shutter angle will allow it. A 180° shutter angle is considered normal.

So for instance, at 24 fps the frame interval value is 0.04167 second ( = 1⁄24 ). Using an exposure time of 1⁄50 second gives a shutter angle value of 173°, very close to 180° (normal motion blur effect).

Tight shutters create a stuttering stop-motion animation look that has become popular in action and war films. In particular, tight shutters are used to capture particles flying through the air, such as dirt from an exploding mortar.

Motion blur is affected by the exposure time as it is governed by the frame rate and shutter angle.

On most film cameras the shutter angle is changed by removing the lens and adjusting the shutter with a special tool. This cannot be done while the camera is operating. Some cameras such as the Arriflex 435ES can modify their shutter angle during the shot. This is sometimes referred to as an electronic shutter. An electronic shutter can compensate for the exposure change caused by a speed ramp without changing the aperture and affecting depth of field.

Other types of shutter adjustments, such as an out-of-phase shutter and a fluttering shutter, are also possible. Normally the film is held steady in the gate whenever it is exposed to light. Special shutter adjustments allow the film to be exposed while the camera mechanism is actually moving the film to the next frame. In the film Saving Private Ryan, cinematographer Janusz Kamiński used such a shutter adjustment to give his film the look of World War II newsreel photography. Previously, this effect could only be achieved by purposefully mis-adjusting the timing belt of the film advance mechanism in the camera. However, several manufacturers now provide accessories to electronically control the phase relationship of the shutter and film advance mechanisms. One such device is the Timing Shift Box available for the above mentioned ARRI 435 series.[citation needed]

Electronic equivalent

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Many video cameras also provide the ability to adjust their shutter. In most cases the camera does not have an actual mechanical shutter. Instead, this adjustment controls the amount of time that the electronic sensor collects light in order to create each successive image. Because electronic cameras do not need to mechanically advance film, it is possible for the shutter to be open for nearly the entire period of each successive frame. At 24 frames per second, it is possible to expose a frame for nearly 1⁄24 second, achieving longer motion blur otherwise impossible to achieve on film at sync sound speeds.

It is even possible for the shutter to be open for multiple frames, far beyond that possible with a 360° shutter angle. One example is the Sony PD170 where the shutter can be set as low as 1⁄3 second; accumulating light across 10 frames (at a frame rate of approximately 30 frames of 60 interlaced fields per second for the NTSC version of the camera and 25 of 50 for the PAL version)

The term electronic shutter is often used to describe the electronic process of controlling exposure time on a light sensor. The same term is also used in film cameras to refer to a mechanical rotary shutter which can adjust its shutter angle electronically while shooting.

Rotary shutters on still cameras

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Rotary shutter in an Agfa Caja 44

While the vast majority of rotary shutters are naturally used on motion-picture cameras (as well as projectors), there were some still cameras that employed this type of shutter, notably the Univex Mercury rangefinder and the Olympus Pen F SLR. Both of these cameras were half-frame 35mm cameras (frame size 18 mm × 24 mm). The rotary shutter proved to be very simple to construct, accurate and reliable in these cameras. Though, in the case of the Univex, it resulted in an apparent hump on top of the camera to cover the shutter disc.

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Rotary disc shutter

View on Grokipedia
from Grokipedia
A rotary disc shutter is a mechanical device used primarily in motion picture cameras and projectors, consisting of a circular disc that rotates continuously in front of the film gate or lens, featuring one or more cut-out sectors or openings that intermittently allow to expose each frame of film. The disc typically spins at a speed synchronized with the camera's —such as 24 frames per second for standard —where each half-rotation exposes a single frame, with the duration of exposure controlled by the angular width of the opening, often set to 180 degrees to produce natural motion blur. This shutter mechanism first notably appeared in Thomas Edison's Kinetograph camera in 1891 as a key innovation in early , enabling the smooth, sequential capture of moving images by replacing earlier, less efficient slit or guillotine-style shutters. By the early , rotary disc shutters became standard in professional cameras, such as 16mm and 35mm models, due to their simplicity, reliability, and ability to operate at consistent speeds without that could blur . In operation, a motor drives the disc via gears, positioning it between the lens and film plane; as the opening aligns with the , light passes through to expose the stationary , after which the opaque portion blocks light to advance the frame. While largely superseded by electronic shutters in , the rotary disc design persists in specialized applications, including and vintage restoration, where its precise mechanical timing ensures artifact-free exposure. Its legacy influences modern shutter concepts in , allowing filmmakers to replicate the aesthetic of analog motion blur.

Introduction

Definition and principles

A rotary disc shutter is a mechanical device used in cameras, consisting of a rotating disc featuring a sector-shaped opening that intermittently exposes the film or to by spinning in front of the film gate or . The disc blocks except during the brief alignment of its opening with the , thereby controlling the duration of exposure for each frame. The fundamental operating principles involve either continuous rotation for ongoing frame sequences or a single rotation per exposure in simpler setups, with the rotation speed directly determining the . Exposure occurs solely when the sector opening passes across the light path, while the opaque portions of the disc prevent illumination otherwise; in basic designs, this yields typical exposure times ranging from 1/30 to 1/60 second. The mechanism is powered by springs, rubber bands, or electric motors to achieve the necessary rotational velocity, ensuring precise timing synchronized with advancement where applicable. Geometrically, the disc may be semicircular or fully circular with a cutout sector, where the angular extent of the opening defines the proportion of each dedicated to exposure. The shutter angle, representing this proportion, typically measures the exposure relative to the full cycle, such as 180 degrees for half- exposure in standard configurations.

Historical context

The first appeared in the late during the transition to more sensitive dry plates, which demanded faster and more precise exposure control beyond simple lens caps. Early designs emerged around 1880, with notable innovations including Chadwick's rotary shutter for cameras. By 1885, popular elastic band-powered models were introduced by manufacturers such as Lancaster and Shew, marking the shutter's initial commercialization in simple hand-held cameras. In the late 19th and early 20th centuries, rotary disc shutters gained widespread adoption due to their mechanical simplicity, reliability, and low cost, integrating seamlessly into box cameras and nascent cine equipment. They became standard in inexpensive roll-film box cameras, such as models from the 1890s onward, enabling amateur photographers to achieve exposures of 1/30 to 1/60 second without complex mechanisms. In motion picture technology, the shutter's design facilitated intermittent film advancement in early cinema projectors and cameras from the 1880s to 1900s, supporting the rise of 35mm and 16mm formats. The mid-20th century represented the peak of rotary disc shutter sophistication and production scale. Massive manufacturing occurred for budget box cameras during the to , with millions of units produced for consumer markets. A high point came in 1963 with the half-frame SLR, which featured an innovative rotary capable of speeds up to 1/500 second and full flash synchronization, demonstrating the mechanism's potential in advanced reflex designs. Post-1960s, rotary disc shutters declined in advanced still photography, largely supplanted by more versatile focal-plane and shutters that offered greater speed ranges and compatibility with larger formats. Their bulkiness proved impractical for full-frame and medium-format cameras as sensor sizes grew. However, they persisted in amateur cine cameras, including Super 8 models, and low-cost still cameras into the 1980s due to enduring simplicity in budget applications.

Design and mechanism

Key components

The rotary disc shutter features a primary rotating disc, typically constructed from metal or lightweight , designed as either a semicircular shape or a full disc with a sector-shaped cutout to facilitate exposure control. This disc is mounted on a central shaft or , often supported by bearings for precise . The drive mechanism includes options such as a for tensioning the disc, a for powering in simpler designs, or a geared motor in more advanced setups. Supporting structural elements encompass the film gate or aperture mask, which serves to precisely align the exposure area with the lens and film plane through a fixed frame or . Tension regulators, such as flat springs or braking levers, maintain uniform rotational consistency. In cine camera variants, gears interlock with the disc's drive to coordinate with film advancement rates. Material choices emphasize durability and functionality, with early constructions relying on brass or steel for the disc and associated metal parts to withstand mechanical stress.

Operation and shutter angle

The operation of a rotary disc shutter begins with the light path from the lens being blocked by the opaque portion of the rotating disc positioned in front of the film gate. In still cameras, the mechanism is typically spring-driven and cocked during film advance, with the release lever triggering a single rotation of the disc, during which the open sector sweeps across the gate to expose the stationary film. In motion picture cameras, the disc spins continuously at a speed synchronized to the frame rate, ensuring the film advances intermittently such that each frame is stationary precisely when the open sector aligns with the gate for exposure, followed by blocking during the pull-down phase. This sequence—film positioning under cover, exposure via the opening, and subsequent blocking—repeats for each frame in cine applications. The shutter defines the portion of the disc's rotation during which light reaches the film, measured in degrees as the of the open sector relative to a full 360° . This directly influences the exposure duration per frame, calculated as the fraction of the frame period: for a given , the exposure time TT is given by the formula
T=θ360∘×1fT = \frac{\theta}{360^\circ} \times \frac{1}{f}
where θ\theta is the shutter in degrees and ff is the frames per second (fps). For instance, a common 180° shutter at 24 fps results in an exposure of 1/481/48 second, producing natural motion blur in footage. In advanced cine models, variable shutter angle mechanisms enable precise exposure control by adjusting the open sector's size, such as through movable blades or sectors integrated into the disc. Similarly, the Zeiss Ikon AK16 incorporates an adjustable sector opening in its rotary disc to vary the angle mechanically.

Applications

In still cameras

Rotary disc shutters found widespread use in budget still cameras, particularly box models like the Brownies produced from the early 1900s through the 1950s, where they provided fixed exposure speeds of approximately 1/30 to 1/60 second. These simple mechanisms relied on a spring or drive to enable a single rotation per exposure, activated by a basic , making them ideal for amateur photographers seeking affordable, point-and-shoot simplicity. Millions of such cameras were manufactured, with alone selling over 1.2 million Brownie units by 1905, democratizing for the masses starting in the early 20th century. In more advanced still photography applications, rotary disc shutters were adapted for half-frame single-lens cameras, such as the 1963 , which featured a cloth-covered focal-plane disc for quieter operation during exposure. Some folding cameras also incorporated rotary designs with adjustments to support timed or modes, allowing for longer exposures beyond the fixed instantaneous speed. The primary advantages of rotary disc shutters in still cameras included their reliability and low , which suited mass-produced budget designs with minimal mechanical complexity and low vibration during operation. However, their fixed speeds limited versatility, rendering them unsuitable for capturing high-speed action where faster shutter rates were needed to freeze motion.

In motion picture cameras

Rotary disc shutters became a standard mechanism in motion picture cameras across 8mm, 16mm, and 35mm formats, providing intermittent exposure by allowing light to reach the film only when a frame was stationary in the , between each pulldown or frame advance. In cameras like the Zeiss Ikon AK16, a 16mm model from the mid-20th century, the rotary disc facilitated precise exposure control during continuous filming, essential for both professional and . This design enabled the illusion of smooth motion in projection by blocking light precisely during the film's intermittent movement, a principle integral to early 20th-century silent films and persisting through movie making. The shutter's continuous rotation was synchronized with the camera's claw or sprocket-driven intermittent film transport mechanisms, ensuring the disc opened for exposure exactly when the film paused and closed during the brief advance to the next frame. A typical 180° shutter angle, where the open sector covers half the disc's rotation, produced natural motion blur at standard 24 frames per second (fps), equivalent to a 1/48-second exposure per frame, mimicking the fluidity of perceived motion without excessive strobing. In professional models from the onward, variable shutter angles—ranging from 45° for sharper, less blurred images to 270° for increased exposure and softer motion—allowed cinematographers to adjust for creative effects or conditions without altering frame rates. Following the advent of sound films in the late , rotary disc designs emphasized balanced rotation to minimize operational noise, making them suitable for on-set audio recording in quieter, self-blimped camera bodies.

Equivalents and variants

Electronic equivalents

The primary electronic equivalent to the rotary disc shutter is the global shutter, which exposes the entire simultaneously, mimicking the full-frame exposure sweep of a mechanical rotary disc while eliminating distortions like those from readout. This approach is particularly valued in professional for capturing fast motion without skew or wobble artifacts, as seen in high-end cameras such as RED's Komodo and V-RAPTOR models, which integrate global shutter sensors to deliver cinema-quality imagery. In 2024, RED released the V-RAPTOR [X] series, the first large-format global shutter cinema cameras, further advancing emulation of rotary disc exposure effects. In electronic terms, global shutters operate through pixel-level charge reset and parallel readout across the , bypassing any physical components for light control. This allows precise timing adjustments to simulate variable shutter angles; for instance, a 180° equivalent can be achieved by setting exposure to 1/48 second at 24 frames per second, replicating the motion blur profile of traditional film exposures. Compared to mechanical rotary discs, global shutters offer key benefits including complete silence during operation, absence of mechanical wear or vibration, and the potential for full 360° exposure without physical obstructions. These advantages facilitated a transition in starting in the late 1990s, as early electronic systems evolved to emulate the natural motion blur and frame blending of film rotary shutters for a more authentic "."

Mechanical variants

Mechanical variants of the rotary disc shutter include modifications that allow for adjustable exposure control without altering the speed, such as sector adjustments in cine cameras. These typically involve a secondary disc or overlapping sector that varies the opening , enabling filmmakers to control light exposure per frame while maintaining consistent frame rates. For instance, in 16mm motion picture cameras like the Zeiss AK16, the shutter can be mechanically adjusted to range from 90 to 270 degrees, optimizing motion blur and brightness independently of . To reduce operational noise in single-lens reflex cameras, muffled rotary disc designs emerged, particularly in the Universal Mercury II from the late . This camera employs a large rotating focal-plane disc shutter housed in a dedicated top-mounted chamber, producing a subdued "muffled " sound rather than a sharp click, making it suitable for discreet shooting. While not explicitly cloth-covered, the enclosed mechanism and aluminum construction contribute to its quiet operation, distinguishing it from noisier metal focal-plane alternatives of the era. Related mechanical types parallel the rotary disc but use -driven plates instead of continuous spinning discs. Rotary blade shutters, common in early box cameras, feature a single pivoted plate with a hole that sweeps across the lens via spring tension released by a , operating on an "over-center" for bidirectional motion. Examples include the Six-16 from 1938, where a kidney-shaped plate provides instantaneous exposures limited to fixed speeds like 1/40 second, differing from disc variants by relying on a single oscillatory sweep rather than rotational inertia. Primitive rotary shutters from the often used rubber bands for power, marking an early evolution toward self-contained mechanisms. The Lancaster Rotary shutter of 1885, for example, employed a rubber-band drive to rotate a sector plate across the lens, with adjustable tension for speeds from instantaneous to timed exposures, as seen in Instantograph field cameras. This band-powered design swept light in a similar arc to later discs but required manual resetting and was prone to inconsistent tension over time.

References

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  2. https://www.dpreview.com/news/8244457153/video-a-1000fps-look-at-how-a-16mm-motion-picture-camera-works
  3. https://www.whatdigitalcamera.com/technical-guides/technology-guides/advanced-technology-guide-focal-plane-shutter-82027
  4. https://www.filmatlas.com/entry/10
  5. https://www.robertcmorton.com/142-years-of-camera-evolution/
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  7. https://patents.google.com/patent/US4942415A/en
  8. https://www.red.com/red-101/global-rolling-shutter
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  10. https://specialised-imaging.com/wp-content/uploads/2025/02/SI_RA__Dissecting_Time-1.pdf
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  20. https://www.youtube.com/watch?v=Ev-VChXpoZs
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  25. http://dougkerr.net/Pumpkin/articles/Kodak_film_transport.pdf
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  30. https://www.alisterchapman.com/2013/01/18/the-obsession-with-using-shutter-angle-on-an-electronic-video-camera/
  31. https://connealy.blogspot.com/2012/10/rotary-shutters.html
  32. https://support.red.com/hc/en-us/articles/360022436434-Global-Rolling-Shutters
  33. https://www.technexion.com/resources/global-shutter-vs-rolling-shutter-in-embedded-vision/
  34. https://petapixel.com/2024/01/26/red-launches-worlds-first-large-format-global-shutter-cine-cameras/
  35. https://www.red.com/v-raptor
  36. https://andor.oxinst.com/learning/view/article/rolling-and-global-shutter
  37. https://fstoppers.com/gear/difference-between-different-camera-shutters-660104
  38. https://www.videomaker.com/how-to/shooting/camera-settings/what-is-shutter-angle-and-why-is-it-important/
  39. https://www.photo.net/forums/topic/146735-quiet-shutters/
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  41. http://licm.org.uk/livingImage/Kodak_Brownie_Six16.html
  42. https://throughavintagelens.com/2010/08/shutters/
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