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Tuesday, April 29, 2014

DPP Solutions: The Lingo

Decoding the jargon of motion capture


This Article Features Photo Zoom
Sony PMW-F55


Many photographers who are entering the realm of motion capture have encountered an unexpected problem: the terminology. It's like Vincent describing Europe to Jules in Pulp Fiction—everything is just a little bit different. In this brief article, we outline a few of the differences you may find confusing if you have limited or no motion-capture experience.


Tokina AT-X 11-16mm T3.0
Cinema Lenses
People talk about a "cinematic look" a lot these days, and the conversation frequently centers around the lenses. Cinema lenses have a number of key differences from still photography lenses. That's because primes and zooms built specifically for video have different requirements than still lenses. Oversized, "declicked," freely rotating barrels are included for making subtle changes to focus and aperture while recording a take. Often, the casings are also big enough to add focusing marks to be able to rack focus between two subjects during a take. They also have geared focus for working with precise manual-focusing systems like follow-focus units. Still lenses, on the other hand, are built to be as efficiently compact as possible, so they're lighter and the rotation is much more rapid.

Though comparable, cinema lenses also use T-stops rather than ƒ-stops to denote aperture. These T-stops and barrel diameters are often matched across a range of lenses to minimize any changes that must be made with lens peripherals like matte boxes, follow-focus units or rig systems while swapping focal lengths during filming. (See below for an explanation of T-stops.)


Canon EOS 5D
Even with high-definition video, it's recommended that you stay with professional-level lenses, and that's a 2-megapixel file compared to an 8-megapixel file with 4K. Resolution limits for a lens are shown through MTF charts, which use line-mm pairs to compare two distinct lines and the point at which they converge in a set of optics. At this point, they can no longer be discerned as separate points of detail, the resolution limit of the lens.

Still cameras pack a lot of resolution into sensors, and lenses need to be capable of resolving to these levels. Canon's family of EF- and PL-mount Cinema Prime lenses are designed for 4K resolution. Currently, the lineup includes compact zooms, primes and CINE-SERVO lenses, which have a detachable Servo Drive Unit for automatic zooming during news-gathering types of events or quiet manual zooming during filming. Their set of Cinema Primes currently ranges from the CN-E14mm T3.1 L F to the CN-E135mm T2.2 L F.

Tokina is entering the cinema lens line with a few zoom models, the AT-X 11-16mm T3.0, 16-28mm T3.0 and 50-135mm T3.0. Each is based on their respective still lenses of the same focal lengths, but they feature manual focusing and better ergonomics for cinematography, as well as metrics for making focus changes. They will be available in Canon EF and PL mounts.

 

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