How a Camera Works

How a Camera Works

Understanding how a camera works is essential for any VFX artist. When you are trying to match a 3D camera to real footage, you need to know about sensor size, focal length, focus distance, and exposure. Every physical camera captures light through a lens and projects it onto a sensor or film plane. The relationship between these components determines exactly what the final image looks like.

The sensor or film size is one of the most important specifications. A full frame sensor is 36 by 24 millimeters, the same size as a frame of 35mm film. A Super 35 sensor is smaller, about 24 by 13 millimeters, which is common in cinema cameras. The size of the sensor directly affects the field of view. Put the same lens on a full frame and a Super 35 camera, and the Super 35 will show a narrower view because it is effectively cropping the image.

Exposure is controlled by three things: aperture, shutter speed, and ISO. Aperture is the opening in the lens that lets light in, measured in f-stops. A lower f-number means a wider opening and more light. Shutter speed is how long the sensor is exposed to light. In video, this is usually related to the frame rate. ISO is the sensitivity of the sensor. Higher ISO gives you a brighter image but adds noise. For VFX, you want the cleanest image possible, so a low ISO is preferred.

Focus is another critical factor. When you track a shot, the camera tracking software needs to know the focal length and the focus distance to solve the camera motion correctly. Some shots have rack focus where the focus shifts from one subject to another, and this can be very difficult to track because it changes the optical characteristics of the lens. Cinematographers often avoid focus pulls on VFX heavy shots to make the tracking easier.

For camera tracking in VFX, you need metadata about the camera used to shoot the plate. Knowing the sensor size, the lens used, and any settings like anamorphic squeeze is essential for getting an accurate solve. This is why VFX supervisors create camera reports on set, documenting every piece of information that will help the tracking team later. A well documented shot is much easier to track than one where you have to guess the camera parameters.