Have a tech question? Please feel free to send us an email, and we’ll do our best to post a response.

Tech Tip	Subject
#1	Charging Batteries
#2	Aspect Ratios and Formats
#3	Shooting for HD
#4	An Introduction to 3–Perf

Tech Tip #4

An Introduction to 3–Perf

Shrinking budgets are something all of us in the production community can relate to. Almost paradoxically, as productions become more and more complex the pressure only seems to increase to deliver more, faster and on a tighter budget. Fortunately, advances in motion picture technology continue to offer new solutions to meet these narrowing constraints and deliver more for less. One such solution is the 3-perforation motion picture camera movement (3-Perf), a simple but effective adaptation of existing 35mm motion picture camera technology that offers a 25% savings in raw film stock consumption (and processing, concordantly) with no reduction in image quality. This article will explain how 3-Perf works, as well as the advantages (and disadvantages) associated with its use.

First, some terms:

Movement

• The physical mechanism inside a motion picture camera that transports the film past the shutter to be exposed.  In most cameras this is a modular component that can be removed and replaced in its entirety, though the difficulty of this procedure differs from camera to camera.
  

Registration

• The first phase of the film transport cycle in a motion picture camera. During this phase, the film is pressed against the gate and the shutter cleared to allow light passing through the lens to strike the film and expose it. Most contemporary motion picture cameras hold the film steady during this phase by inserting one or more registration pins into the film's perforations while it is exposed to ensure a consistent picture.

Pulldown

• The second phase of the film transport cycle, during which the gate is covered by the shutter to block light from the lens and the film is advanced by one frame. This is accomplished by the pulldown claws, metal pins that engage the perforations in the film and draw it past the gate.

Aperture

• The physical area of the empty part of the gate through which light passes to expose the film. The size of the aperture can be adjusted in most cameras to limit the area of film exposed.

Super35

• A camera format in which the lens mount is optically re-centered to take advantage of negative area originally reserved for an optical soundtrack (now unused since the advent of digital sound). This provides more available negative area for the image and improves picture quality.

Aspect Ratio

• The ratio of width to height in a motion picture image, usually expressed as units width per one unit height (e.g. 1.78:1 or 2.35:1).

I. A Brief History of Motion Picture Camera Movements
Since its standardization in the early part of the 20th century, the basic mechanical functions of a 35mm motion picture camera have remained remarkably unchanged. Sophisticated contemporary electronics aside, a motion picture camera remains at its core a lightproof box with a lens on it through which film is passed one frame at a time to be exposed. The film is transported from the magazine through the camera body by means of sprockets and/or rollers that interface with perforations punched into the sides of the film (64 per side per foot) until it reaches the gate, where the actual exposure takes place. In a traditional camera movement, once at the gate the film is advanced four perforations at a time by the pulldown claw(s) and held against the aperture of the gate while the shutter swings open to expose it and create one frame. Once exposure is complete, the shutter closes and the film advances by another four perforations to repeat the cycle and create the next frame.

In the early days of cinematography before the advent of sync sound (and the concordant need for an optical sound track on the film), each exposed frame utilized the full width of the negative to record an image roughly four perforations high with an aspect ratio of 1.33:1, conventionally known today as "Full Frame" or "Silent" aperture. Once optical sound recording appeared this image area was reduced in both width and height to make room for the sound track alongside the image, yielding the Academy 1.37:1 aspect ratio common for theatrical production up until the 1950's when various anamorphic widescreen aspect ratios were adopted to compete with television.

Up until this point the 4-perforation camera movement remained efficient because all of the conventionally used aspect ratios, when combined with the optical soundtrack, utilized nearly all of the available negative area allowed by the silent aperture.

Anamorphic was not without its disadvantages, however; the lenses were (and still are) slow, heavy and expensive, and by the 1970's filmmakers were increasingly electing to shoot 1.85:1 widescreen using spherical (non-anamorphic) lenses. This method offered the advantage of lighter, faster, cheaper (and often optically superior) spherical lenses instead of the cumbersome anamorphics, but because it utilized less of the negative area (the top and bottom of the camera aperture matted off to create the more rectangular aspect ratio) it had the concordant disadvantages of lower picture quality than anamorphic and inefficient use of the negative since only a fraction of the total available imaging area was used. The development of Super35, digital intermediate and more advanced film emulsions have improved picture quality with spherical widescreen to the extent that it is no longer considered significantly inferior to anamorphic in that respect, but the inefficient use of negative remains a concern. Originally conceived of in Russia and developed by numerous cinematographers and camera companies since, 3-Perf offers a solution to that inefficiency.


II. 3-Perf: Theory, Applications and Advantages
The basic premise of 3-Perf is a simple one: because spherical widescreen aspect ratios do not require a full four perforations' worth of negative area, when shooting in these aspect ratios a modified camera movement is used that advances the film three perforations per pulldown stroke instead of four. This reduces film consumption by 25%, which translates into a 25% savings in the cost of stock purchase and processing. For feature films and episodic television, which routinely consume hundreds of thousands of feet of film in the course of production, that cost savings can be substantial. Reduced film consumption also means more filming time per magazine, which gives directors and cinematographers more creative flexibility by allowing potentially longer takes (useful for Steadicam and handheld situations where 400' magazines must be used) and saving time on set by reducing the frequency of camera reloads. 3-Perf also allows the camera to run more quietly since the film transport mechanism doesn't need to run as quickly, allowing the camera to get closer to the action without sound problems.


III. Limitations of 3-Perf
Though 3-Perf does offer many advantages over traditional 4-Perf filming, unfortunately it is not without its own drawbacks and limitations. First and foremost, having been designed for use with widescreen aspect ratios 3-Perf is most effective only when shooting in a 1.78:1 aspect ratio or wider. While this makes it ideally suited to productions intended for HDTV delivery, the standard definition NTSC aspect ratio of 1.33:1 can only be achieved in 3-Perf by shrinking the image area to fit within the reduced vertical dimension allowed by 3-Perf. While still acceptable with slower, fine-grained films, this can lead to undesirably apparent film grain with high speed emulsions. In situations where 3-Perf originated material will be delivered as a film print (i.e. theatrical exhibition or film dailies screening) an additional optical printing step is necessary to transpose the 3-Perf camera original onto a projection-capable 4-Perf interpositive or print.

Not all motion picture cameras can be converted to 3-Perf, and among those that can the groundglasses and aperture plates/masks for certain aspect ratios may not be available. Within the Arri line of cameras, only the 235, 535 and Arricam can be modified for 3-Perf filming. The Arriflex 435 is available with a 3-Perf movement but cannot be changed between 3-Perf and 4-Perf; the movement is permanently installed and a complete new camera body must be ordered if 3-Perf shooting is required. 3-Perf aspect ratio choices are limited to 1.33:1. 1.66:1. 1.78:1 and 1.85:1 in Regular 35 with 1.78:1, 1.85:1 and 2.35:1 available in Super35. Similarly, telecine and optical printing systems require special modification to handle 3-Perf and may not be available at all labs and postproduction facilities.

The final and most significant limitation of 3-Perf is its limited availability: as of this writing only a handful of west-coast camera rental companies have the capability to perform the necessary modifications to convert a camera to 3-Perf in-house, a difficult process that requires specialized training, expensive precision tools and four to eight hours of work depending on the complexity of the camera and the skill of the technician. The 3-Perf movements themselves also quite expensive, often costing nearly as much as a complete camera body, so even those camera rental companies that do carry them keep a limited number on-hand. Companies without the necessary tools and parts must send their cameras back to the manufacturer for conversion and incur the additional costs of shipping, renting the replacement movement and paying for the conversion, all of which must be repeated to return the camera to 4-perf upon completion of a production. These costs are passed on to the production renting the equipment such that it often doesn't make economic sense to pay for the conversion unless the production stands to save substantial film and processing costs by doing so. It is always essential when considering 3-Perf shooting to consult with the camera rental company and postproduction facility well in advance of commencing production to confirm availability/compatibility and ensure sufficient time to make the modifications necessary for 3-Perf shooting and telecine.

Article and Illustrations © Schumacher Camera 2006