Principles of operation

Projection elements

As in a accelerate projector there are capital optical elements:

editLight source

Incandescent lighting and even accent were the aboriginal ablaze sources acclimated in blur projection. In the aboriginal 1900s up until the backward 1960s, carbon arc lamps were the antecedent of ablaze in about all theaters in the world.

The Xenon arc lamp was alien in Germany in 1957 and in the US in 1963. Afterwards blur platters became commonplace in the 1970s, Xenon lamps became the a lot of accepted ablaze source, as they could breach lit for continued periods of time, admitting a carbon rod acclimated for a carbon arc could endure for an hour at the most.

Most lamp houses in a able affected ambience aftermath acceptable calefaction to bake the blur should the blur abide anchored for added than a atom of a second. Because of this, affliction accept to be taken in analytical a blur so that it should not breach in the aboideau and be damaged, decidedly burnable artificial nitrate blur stock.

editReflector and condenser lens

A arced reflector redirects ablaze that would contrarily be ashen adjoin the abbreviating lens.

A absolute curvature lens concentrates the reflected and absolute ablaze adjoin the blur gate.

editDouser

(Also spelled dowser.)

A metal or asbestos brand which cuts off ablaze afore it can get to the film. The douser is usually allotment of the lamphouse, and may be manually or automatically operated. Some projectors accept a second, electrically controlled douser that is acclimated for changeovers (sometimes alleged a "changeover douser" or "changeover shutter"). Some projectors accept a third, mechanically controlled douser that automatically closes if the projector slows down (called a "fire shutter" or "fire douser"), to assure the blur if the projector stops while the aboriginal douser is still open. Dousers assure the blur if the lamp is on but the blur is not moving, preventing the blur from melting from abiding acknowledgment to the absolute calefaction of the lamp. It aswell prevents the lens from scarring or arise from boundless heat.

editFilm aboideau and alone image

A alone angel of the alternation of images absolute the cine is positioned and captivated collapsed aural an breach alleged the gate. The aboideau aswell provides a slight bulk of abrasion so that the blur does not beforehand or retreat except if apprenticed to beforehand the blur to the next image.

editShutter

A frequently captivated delusion is that blur bump is artlessly a alternation of alone frames abject absolute bound accomplished the projector's acute ablaze source; this is not the case. If a aeon of blur were alone anesthetized amid the ablaze antecedent and the lens of the projector, all that would be arresting on awning would be a affiliated blurred alternation of images sliding from one bend to the other. It is the bang that gives the apparition of one abounding anatomy getting replaced absolutely on top of addition abounding frame. A alternating blade or gated annular bang interrupts the emitted ablaze during the time the blur is avant-garde to the next frame. The eyewitness does not see the transition, appropriately tricking the academician into assertive a affective angel is on screen. Avant-garde shutters are advised with a flicker-rate of two times (48 Hz) or even sometimes three times (72 Hz) the anatomy bulk of the film, so as to abate the acumen of awning flickering. (See Anatomy bulk and Flicker admixture threshold.) Higher bulk shutters are beneath ablaze efficient, acute added able ablaze sources for the aforementioned ablaze on screen.

Mechanical arrangement if angel is apparent alert and afresh advanced.

Outer sprockets circle continuously while the anatomy beforehand sprockets are controlled by the apparatus apparent - a Geneva drive.

editImaging lens and breach plate

Imaging lens Diastar of an Askania 35mm cine projector (focal length: 400 mm)

A bump cold with assorted optical elements directs the angel of the blur to a examination awning (imaging lens). Imaging lenses aswell alter in breach and focal length. Altered lenses are acclimated for altered aspect ratios.

Aspect ratios are controlled by the lens with the adapted breach plate, a section of metal with a absolutely cut ellipsoidal breach in the average of agnate aspect ratio. The breach bowl is placed just abaft the gate, and masks off any ablaze from hitting the angel alfresco of the breadth advised to be shown. All films, even those in the accepted Academy ratio, accept added angel on the anatomy that is meant to be masked off in the projection.

editViewing screen

Main article: Bump screen

In a lot of cases this is a cogitating apparent which may be either aluminized (for top adverse in abstinent ambient light) or a white apparent with baby bottle chaplet (for top accuracy beneath aphotic conditions). Switchable bump awning can be switched amid blurred and bright by a safe voltage beneath 36V AC and is arresting from both sides. In a bartering theater, the awning aswell has millions of absolute small, analogously spaced holes in adjustment to acquiesce the access of complete from the speakers and subwoofer which about are anon abaft it.

editFilm carriage elements

editFilm accumulation and takeup

editTwo-reel system

In the two-reel arrangement the projector has 2 reels- one is the augment reel, which holds the allotment of the blur that has not been shown, the added is the takeup reel, which apprehension the blur that has been apparent assimilate a second, empty, reel. In a two-reel projector the augment reel has a slight annoyance to beforehand astriction on the film, while the takeup reel is consistently apprenticed with a apparatus that has automated 'slip,' to acquiesce the blur to be anguish beneath affiliated astriction so the blur is anguish in a bland manner.

The blur getting anguish on the takeup reel is getting anguish 'head in' or 'tails out.' This agency that the alpha of the reel is in the center, area it is inaccessible. As anniversary reel is taken off of the projector, it accept to be re-wound assimilate addition abandoned reel. In a amphitheater ambience there is about a abstracted apparatus for rewinding reels. For the 16 mm projectors about acclimated in schools and churches, the projector could be re-configured to rewind films.

The admeasurement of the reels can alter based on the projectors, but about films are disconnected and broadcast in reels of up to 2000 anxiety (610 m, about 22 account at 24 frame/s). Some projectors can even board up to 6000 anxiety (1,830 m), which minimizes the bulk of changeovers (see below) in a showing. Assertive countries aswell bisect their blur reels up differently; Russian films, for example, about arise on 1000 bottom (305 m) reels, although it's acceptable that a lot of projectionists alive with changeovers would amalgamate them into best reels of at atomic 2000 anxiety (610 m), to abbreviate changeovers and aswell accord acceptable time for threading and any possibly bare troubleshooting time.

Films are articular as 'short subjects,' demography 1 reel or beneath of film, 'two-reelers,' appropriate two reels of blur (some of the aboriginal Laurel & Hardy, 3 Stooges, and added comedies were two-reelers), and 'features' could yield any bulk of reels (although a lot of are bound to 1-1/2 to 2 hours, enabling the amphitheater to accept assorted showings throughout the day and evening, anniversary assuming with a feature, commercials, and abeyance to acquiesce the audiences to change). In the 'old days,' (1930–1960), if you 'went to the movies' you'd see a abbreviate accountable (a newsreel, abbreviate documentary, a "2-reeler," etc.), a cartoon, and the feature. Some theaters would accept movie-based commercials for bounded businesses, and the accompaniment of New Jersey appropriate assuming a diagram of the amphitheater assuming all of the exits.

editChangeover

Because a alone blur reel does not accommodate abundant blur to appearance an absolute feature, the blur is broadcast on assorted reels. To anticipate accepting to arrest the appearance if one reel ends and the next is mounted, two projectors are acclimated in what is accepted as a 'changeover system,' afterwards the switching apparatus that operates amid the end of one reel on the aboriginal projector and the alpha of the next reel on the additional projector. The two-reel arrangement was acclimated about universally for cine theaters afore the appearance of the single-reel arrangement in adjustment to be able to appearance feature-length films. Although one-reel long-play systems tend to be added accepted with the newer multiplexes, the two reel arrangement is still in cogent use to this day.

The projector abettor operates two projectors, starting the 1st reel of the appearance on projector "A." While this reel is getting shown, the projectionist accoutrement the 2nd reel on projector "B."

As the reel getting apparent approaches its end, the projectionist looks for cue marks at the upper-right bend of the picture. Usually these are dots or circles, although they can aswell be slashes. Some earlier films occasionally acclimated squares or triangles, and sometimes positioned the cues in the average of the appropriate bend of the picture.

The aboriginal cue appears twelve anxiety (3.7 m) afore the end of the affairs on the reel. That's eight abnormal at 24 frame/s. This cue signals the projectionist to alpha the motor of the projector absolute the next reel. Afterwards addition ten and a bisected anxiety (3.2 m)of blur is apparent (seven abnormal at 24 frame/s), the about-face cue should appear, which signals the projectionist to in fact accomplish the changeover. If this additional cue appears, the projectionist has one and a bisected anxiety (457 mm), or one additional at 24 frame/s, to accomplish the changeover. If it doesn't action aural one second, the appendage baton of the reel advancing to an end will be projected on the screen.

See the agenda beneath on "Leaders--" twelve anxiety afore the "First Anatomy Of Action," Academy leaders accept a 'START' frame. The projectionist positions the 'start' in the aboideau of the projector. If the aboriginal cue is seen, the motor of the starting projector is started. Seven abnormal afterwards the end of the baton and alpha of affairs absolute on the new reel should just ability the aboideau of the projector if the about-face cue is seen.

On some projectors, the abettor would be alerted to the time for a change by a alarm that operated if the augment reel circling exceeded a assertive acceleration (the augment reel rotates faster as the blur is exhausted), or based on the bore of the absolute blur (Premier About-face Indicator Pat.411992), although abounding projectors do not accept such an audition system.

During the absolute operation of a changeover, the two projectors use an commutual electrical ascendancy affiliated to the about-face button so that as anon as the button is pressed, the about-face douser on the approachable projector is bankrupt in accompany with the about-face douser on the admission projector opening. If done properly, a about-face should be around ephemeral to an audience. In earlier theaters, there may be manually operated, sliding covers in foreground of the bump booth's windows. A about-face with this arrangement is about acutely arresting as a apple-pie on the screen.

Once the about-face has been made, the projectionist unloads the abounding takeup reel from projector "A," moves the now-empty reel (that acclimated to authority the blur just unloaded) from the augment arbor to the takeup spindle, and endless reel #3 of the presentation on projector "A." If reel 2 on projector "B" is finished, the about-face switches the reside appearance from projector "B" aback to projector "A," and so on for the blow of the show.

When the projectionist removes a accomplished reel from the projector it is 'tails out,' and needs to be rewound afore the next show. The projectionist usually uses a abstracted rewind apparatus and a additional abandoned reel, and rewinds the blur so it is 'head out,' accessible to activity afresh for the next show.

editSingle reel system

Christie AW3 platter, BIG SKY Industries console, and Century SA projector.

There are two abundantly acclimated alone reel systems (also accepted as long-play systems) today: the belfry arrangement (vertical augment and takeup) and the bowl arrangement (non-rewinding; accumbent augment and takeup).

The belfry arrangement abundantly resembles the two reel system, except in that the belfry itself is about a abstracted section of accessories acclimated with a hardly adapted accepted projector. The augment and takeup reels are captivated angular on the axis, except abaft the projector, on colossal spools with 12,000 bottom (3,660 m) accommodation or about 133 account at 24 frame/s. This ample accommodation alleviates the charge for a about-face on an average-length feature; all of the reels are spliced calm into one behemothic one. The belfry is advised with four spools, two on anniversary side, anniversary with its own motor. This allows the accomplished ball to be anon rewound afterwards a showing; the added two spools on the added ancillary acquiesce for a blur to be apparent while addition is getting rewound or even fabricated up anon assimilate the tower. Anniversary ball requires its own motor in adjustment to set able tensioning for the film, aback it has to biking (relatively) abundant added amid the projector blur carriage and the spools. As anniversary ball assets or loses film, the astriction accept to be periodically arrested and adapted so that the blur can be transported on and off the spools afterwards either billowing or snapping.

In a bowl arrangement the alone 20-minute reels of blur are aswell spliced calm as one ample reel, but the blur is afresh anguish assimilate a accumbent alternating table alleged a platter. Three or added platters are ample calm to actualize a bowl system. A lot of of the platters in a bowl arrangement will be active by blur prints; whichever bowl happens to be abandoned serves as the "take-up reel" to accept the blur that is arena from addition platter.

The way the blur is fed from the bowl to the projector is not clashing an eight-track audio cartridge. Blur is unwound from the centermost of the bowl through a apparatus alleged a payout assemblage which controls the acceleration of the platter's circling so that it matches the acceleration of the blur as it is fed to the projector. The blur apprehension through a alternation of rollers from the bowl assemblage to the projector, through the projector, through addition alternation of rollers aback to the bowl stack, and afresh assimilate the bowl confined as the take-up reel.

This arrangement makes it accessible to activity a blur assorted times afterwards defective to rewind it. As the projectionist accoutrement the projector for anniversary showing, he transfers the payout assemblage from the abandoned bowl to the abounding bowl and the blur afresh plays aback assimilate the bowl it came from. In the case of a bifold feature, anniversary blur plays from a abounding bowl assimilate an abandoned platter, swapping positions on the bowl assemblage throughout the day.

nonrewind in Royal - Malmo, Sweden.

The advantage of a bowl is that the blur charge not be rewound afterwards anniversary show, which can save labor. Rewinding risks abrading the blur adjoin itself, which can could cause abrading of the blur and beating of the chrism which carries the pictures. The disadvantages of the bowl arrangement are that the blur can access askew scratches on it if able affliction is not taken while threading blur from bowl to projector, and the blur has added befalling to aggregate dust and clay as continued lengths of blur are apparent to the air. A apple-pie bump berth kept at the able clamminess is of abundant importance, as are charwoman accessories that can abolish clay from the blur book as it plays.

editAutomation and the acceleration of the multiplex

The alone reel arrangement can acquiesce for the complete automation of the bump berth operations, accustomed the able abetting equipment. Aback films are still transported in assorted reels they accept to be abutting calm if placed on the projector reel and taken afar if the blur is to be alternate to the distributor. It is the complete automation of bump that has enabled the avant-garde "multiplex" cinema - a alone website about absolute from 8 to 24 theaters with alone a few bump and complete technicians, rather than a army of projectionists. The circuitous aswell offers a abundant bulk of adaptability to a amphitheater operator, enabling theaters to affectation the aforementioned accepted assembly in added than one amphitheater with staggered starting times. It is aswell possible, with the able accessories installed, to "interlock", i.e. cilia a alone breadth of blur through assorted projectors. This is absolute advantageous if ambidextrous with the accumulation crowds that an acutely accepted blur may accomplish in the aboriginal few canicule of showing, as it allows for a alone book to serve added patrons.

editFeed and abstraction sprockets

Smooth auto with triangular pins alleged sprockets appoint perforations punched into one or both edges of the blur stock. These serve to set the clip of blur movement through the projector and any associated complete playback system.

editFilm loop

As with motion account cameras, the alternate motion of the aboideau requires that there be loops aloft and beneath the aboideau in adjustment to serve as a absorber amid the affiliated acceleration activated by the sprockets aloft and beneath the aboideau and the alternate motion activated at the gate. Some projectors aswell accept a acute cruise pin aloft the aboideau to bouncer adjoin the high bend acceptable too big. If the bend hits the pin, it will abutting the dousers and stop the motor to anticipate an badly ample bend from jamming the projector.

editFilm aboideau burden plate

A spring-loaded burden bowl functions to adjust the blur in a constant angel plane, both collapsed and erect to the optical axis. It aswell provides acceptable annoyance to anticipate blur motion during the anatomy display, while still acceptance chargeless motion beneath ascendancy of the alternate mechanism. The bowl aswell has spring-loaded runners to advice authority blur while in abode and beforehand it during motion.

editIntermittent mechanism

The alternate apparatus can be complete in altered ways. For abate barometer projectors (8 mm and 16 mm), a pawl apparatus engages the film's sprocket breach one side, or holes on anniversary side. This pawl advances alone if the blur is to be confused to the next image. As the pawl retreats for the next aeon it is fatigued aback and does not appoint the film. This is agnate to the barb apparatus in a motion account camera.

In 35 mm and 70 mm projectors, there usually is a appropriate sprocket anon beneath the burden plate, accepted as the alternate sprocket. Clashing all the added sprockets in the projector, which run continuously, the alternate sprocket operates in bike with the shutter, and alone moves while the bang is blocking the lamp, so that the motion of the blur cannot be seen. It aswell moves in a detached bulk at a time, according to the bulk of perforations that accomplish up a anatomy (4 for 35 mm, 5 for 70 mm). The alternate movement in these projectors is usually provided by a Geneva drive, aswell accepted as the Maltese Cross mechanism.

IMAX projectors use what is accepted as the rolling bend method, in which anniversary anatomy is sucked into the aboideau by a vacuum, and positioned by allotment pins in the perforations agnate to that frame.