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“Full Frame” Sensors Are Not Necessarily Better for Video

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November 28, 2015

“Full Frame” Sensors Are Not Necessarily Better for Video

Video shooters often desire cameras with larger image sensors because they allow for shooting with longer lenses, which can yield pretty and cinematically shallow depths of field. The cheapest and easiest way to shoot with a large image sensor is to shoot on a DSLR still-camera that also records video. The watershed DSLR filmmaking camera was the Canon 5D Mark II, which boasted a “full frame” image sensor, meaning the sensor was the same size as a single frame of 35mm chemical film. 

But here’s the thing: 35mm motion picture cameras do not use anything close to a full frame of 35mm still film.

A full frame as captured by a 35mm still-camera is 36mm x 24mm in size (the same size as the image sensor on the 5D). But remember: 35mm still cameras expose film horizontally, while motion picture cameras expose film vertically. This simple reorientation means that the size of a 35mm motion picture frame is always going to be smaller than a still frame.

 

But that’s not the only difference!

In 35mm motion picture cameras, a portion of that area is set aside for optical audio stripes that are read by projectors, and since cinematic films are generally “widescreen,” the top and bottom of the frame is cut off compositionally. In reality, the usable frame size of 35mm motion picture film is only 18.6mm x 21.95mm. That’s a “crop factor” of 1.5 and we haven’t even cut in for audio stripes and a widescreen aspect ratio yet!

The good news is that the 35mm “academy aperture” is in a sweet spot as sensor sizes go that allows cinematographers to use a wide range of lenses and have a great deal of control over depth of field. This is partly why many professional cinema camera manufacturers (Arriflex, Black Magic, Red, etc.) produce imaging systems that are closer to the 35mm motion picture format size. 

So the next time you are deciding which camera you want to shoot your movie on, don’t just automatically ask for a “full frame” camera because it sounds cool. Choose a sensor that makes the most sense for you in terms of composition and lens choice.

Ask VCAM staff if you’re looking to learn more!