Digital Single Lens Reflex (DSLR) cameras like the Canon 5D now have the capability of shooting moving pictures which has been a very exciting development to the low budget film maker. In the recent past, because of the high cost of cinema quality movie cameras (upwards of $100,000), lower budget producers used video cameras. Video cameras have been available in a wide range of cost points and had the cost cutting advantage of not needing expensive film and processing. The downside of video has been in its distinctive “video look.” On TV you can clearly see the difference between video – the nightly news, soap operas and talk shows, and shows shot on film – “ER” and “House.”
$120,000 Panavision cinema movie camera
DSLR moving picture images (I hesitate to say, “DSLR video”) look much closer to that of a movie made with the ultra-expensive cinema cameras for several reasons, but the main one is because of a phenomenon known as Depth of Field. All students of photography know the term refers to the depth of focus or how much of the picture is in focus. If you look at the two pictures below, you can see how the narrow depth of field directs the viewer’s eye to the subject. Or put another way; the narrow depth of field “focuses” attention on the subject.
The still image above is an example of a very shallow depth of field. Notice how the subject pops out because the background is a beautiful mush. This was accomplished by having a large lens opening set on the camera.
This image was made using a small lens opening. Notice how the background and the subject are in focus. Portrait photographers and cinematographers generally don’t like to have the background sharp because it can be distracting. Sharpness in a photo or a movie, tells your brain what to pay attention to.
Motion picture cameras and DSLR cameras both are capable of producing images with a very narrow depth of field. This eliminates distracting backgrounds and tells the viewers where they should be looking.
To understand what motion picture cameras have in common and what makes them different from traditional video cameras takes a bit of understanding of the relationship between lens openings and depth of field.
Lens Openings and Depth of Field
One way a photographer or cinematographer can vary depth of field is by changing the size of the lens opening on his camera. The reason lenses have adjustable lens openings is to adjust for bright or dark lighting conditions just like the Iris in our eyes. Bigger lens openings allow more light to pass through to the film and smaller lens openings let less light through.
In addition to exposure, lens openings also have an effect on depth of field. Small lens openings make more of the picture in focus. If you’ve ever seen a picture taken with a pinhole camera you’ll see that everything is in focus because the “lens opening” – a small pinhole – results in the ultimate, wide depth of field. Large lens openings have the opposite effect, giving a very narrow depth of field. This selective focus, narrow depth of field look is the trademark of professional portrait photography and of motion picture cinematography.
Traditional video camera lenses don’t have as big of lens openings as DSLR cameras, thus can’t achieve the same narrow depth of field. DSLR cameras such as the Canon 5D have identical lenses to 35mm cinema cameras with respect to focal length and lens openings, so they both can achieve similar looking images.
Why don’t they simply make video camera lenses with larger openings? To simplify the answer as much as possible, the short answer is this: Due to the physics of optics, it’s not possible to make a lens with an opening whose diameter is greater than the length of the lens. The length of the lens on a camera is related to the size of the film (or of the size of the sensor in a digital camera). Video cameras have small sensors – in the neighborhood of 1/4 or 1/3 inch. Therefore they use shorter lenses, thus are limited to smaller lens openings. DSLR cameras use sensors nearly the same size as a 35mm cinema camera (35mm x 50mm – well over an inch) which dictates the use of longer lenses, which have larger lens openings, which yield a shallow depth of field.