Tuesday, June 8, 2010

EFFECTS OF SENSOR SIZE


A thing that you see in my pictures is that I was not afraid to fall in love with these people.
Annie Leibovitz

Effects of sensor size



Almost all digital cameras, and most digital SLRs, have sensors smaller than a 36 mm x 24 mm frame of 35 mm film. This affects aspects of the captured image and the way the camera is used. These effects include:

  1. Increased depth of field;
  2. Decreased light sensitivity and increased pixel noise;
  3. For digital SLRs, cropping of the field of view when using lenses designed for 35 mm camera;
  4. Lenses may be smaller because they only need to project their image onto a smaller area;
  5. Increased degree of enlargement of the final image.

Depth of field at a given f number increases as the area of film or image sensor decreases. This may have advantages for compact digital cameras intended for taking snapshots; more of the image will be in focus than with a larger sensor and the autofocus system does not need to be as accurate to produce an acceptable image. Photographers often limit depth of field to create certain effects, such as isolating a subject from its background. Cameras with imaging areas smaller than 36 mm x 24 mm require a wider aperture on the lens to achieve the same degree of selective focusing.Depth of field can be minimized by use of large format cameras, which are rarely digital.

Light sensitivity and pixel noise are both related to pixel size, which is in turn related to sensor size and resolution. As the resolution of sensors increase, the size of the individual pixels has to decrease. This smaller pixel size means that each pixel collects less light and the resulting signal ratio must be amplified more to produce the final value. Noise is also amplified and the signal to noise decreases, and the higher noise floor means that less useful information is extracted from the darker parts of the image.

Some digital SLRs use lens mounts originally designed for film cameras. If the camera has a smaller imaging area than the lens' intended film frame, its field of view is cropped. This crop factor is often called a "focal length multiplier" because the effect can be calculated by multiplying the focal length of the lens. For lenses that are not designed for a smaller imaging area whilst using the 35 mm-compatible lens mount, this has the beneficial side effect of only using the centre part of the lens, where the image quality is in some aspects higher. Only expensive digital SLRs and very rarely expensive 'compacts' have 36mm × 24 mm sensors, eliminating depth of field and crop factor problems when compared to 35 mm film cameras.

The smaller sensor size of digital compact cameras means that prints are extreme enlargements of the original image, and that the lens must perform well in order to provide enough resolution to match the tiny pixels on the sensor. Most digital compacts have sensors that exceed the maximum resolution that the lens is capable of delivering. Increased sensor resolution may have affect the image resolution because of increased noise reduction.