Well, that's not a very clear statement of how it works. "Depth of field" is a technical term in photography, describing the amount of an image that is in focus, relative to the out-of-focus areas in front of or behind. This is a function of the aperture (F-stop) of the lens, and the ratio of focal length to sensor size (which also controls perspective, or how wide the angle of view is).
The reason this is important is because out-of-focus areas are a very important visual cue. It isolates the subject of a shot from its surroundings. It is even more important in motion pictures than still photography, where changes in focus are used to move the subject from one person to another in a single shot (watch a conversation in a movie that's shot from one camera for an example). There's even a job, "focus puller", that you'll see in movie credits for the person who adjusts the focus on very large cameras.
Depth of field is strongly correlated to the size of the sensor in digital cameras (and also to lenses). Other inexpensive HD cameras use small sensors, which solve a lot of expensive and difficult technical problems, but at a cost of not being able to do a shallow depth of field (you see the same problem in cell phones and cheap small digital cameras). The big win of Red was to use a full-sized sensor, allowing DoF behavior on par with consumer DSLR cameras. Moreover, the Red cameras had interchangeable lens mounts that could use superb, widely available Canon and Nikon DSLR lenses. This greatly reduced the end user cost.
So basically, unlike cheaper cameras, a Red camera could shoot things that looked like real movies, due to shallow DoF and manual focus control. And it could do so inexpensively. Very disruptive.
This is why the Canon 5DmkII suddenly exploded onto the scene in 2008. It has the same sized sensor as a 35mm film camera (therefore the same depth of field as the RED, more or less)
Its a common misnoma that RED cameras lowered the cost of production. In certain cases it lowered the cost of shooting, but the cost of handling read was at the time ridiculous.
It has the same sized sensor as a 35mm film camera...
Small point of clarification: 35mm still photography cameras have the long side of the image aligned with the sprockets, (864mm² total usable area) while 35 motion photography has the short side aligned with the sprockets. (334mm²) The RED ONE had a 35mm motion photography-sized sensor, (Super 35) the 5Dii had a 35mm still sensor, of course, being principally a still camera.
Thanks, but I'm fully aware what dof means :). I don't understand why typical 2K/HD video cameras couldn't do small depth of field. Nikon D90 could do small depth of focus with a price tag of $900 in 2008 (only 1 year after Red's first camera), and D90 is not a full frame sensor.
The latest generation iPhone can do f/2.0, and it has a pretty small sensor.
It's more than just aperture, though. F/2 on a wide-angle lens like the iPhone won't give you the same impact as F/2 on a telephoto.
Most low-cost HD video cameras have severely compromised lenses, and professional cameras tend to have extremely expensive lenses. Red solved the problem by tapping into the Canon/Nikon lens base.
It's not about field of view (a f/2.0 wide angle and telephoto shot both have the same DOF in terms of actual length - telephoto just appears to have a shallower DOF since the image is cropped.) DOF is actually a physical property of sensor size and aperture size.
The reason this is important is because out-of-focus areas are a very important visual cue. It isolates the subject of a shot from its surroundings. It is even more important in motion pictures than still photography, where changes in focus are used to move the subject from one person to another in a single shot (watch a conversation in a movie that's shot from one camera for an example). There's even a job, "focus puller", that you'll see in movie credits for the person who adjusts the focus on very large cameras.
Depth of field is strongly correlated to the size of the sensor in digital cameras (and also to lenses). Other inexpensive HD cameras use small sensors, which solve a lot of expensive and difficult technical problems, but at a cost of not being able to do a shallow depth of field (you see the same problem in cell phones and cheap small digital cameras). The big win of Red was to use a full-sized sensor, allowing DoF behavior on par with consumer DSLR cameras. Moreover, the Red cameras had interchangeable lens mounts that could use superb, widely available Canon and Nikon DSLR lenses. This greatly reduced the end user cost.
So basically, unlike cheaper cameras, a Red camera could shoot things that looked like real movies, due to shallow DoF and manual focus control. And it could do so inexpensively. Very disruptive.