Optical format
Encyclopedia
Optical format is a measure of the maximum diagonal size of an imaged object in the focal plane
of an optical system. The diagonal size of the imaging sensor (film, CCD
or CMOS
chip etc.) and the optical format of the lens system must be matched.
The optical format is defined as the diagonal length of the sensor (in mm) divided by 16. The result is expressed in inches (not converted to inches!). For instance, a 6.4x4.8 mm sensor has a diagonal of 8.0 mm and therefore an optical format of 8.0/16 = 1/2". The reason why it is expressed in inches is historical: a standard size one inch vidicon tube has only 16 mm of useful imaging area. Therefore 1 inch optics became 16 mm, 1/2 inch optics became 8 mm, etc.
For larger systems the optical format is usually given as rectangular dimensions of the imaging sensor in millimeters, such as 36 x 24 mm in the case of 35 mm film
.
Many image device sheets don't list the actual optical format, but do list the size of their pixels in terms of micrometers, a more helpful equation is to convert the pixel size, and array size, directly to optical format. The equation for this is:
with:
Focus (optics)
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by...
of an optical system. The diagonal size of the imaging sensor (film, CCD
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
or CMOS
Active pixel sensor
An active-pixel sensor is an image sensor consisting of an integrated circuit containing an array of pixel sensors, each pixel containing a photodetector and an active amplifier. There are many types of active pixel sensors including the CMOS APS used most commonly in cell phone cameras, web...
chip etc.) and the optical format of the lens system must be matched.
The optical format is defined as the diagonal length of the sensor (in mm) divided by 16. The result is expressed in inches (not converted to inches!). For instance, a 6.4x4.8 mm sensor has a diagonal of 8.0 mm and therefore an optical format of 8.0/16 = 1/2". The reason why it is expressed in inches is historical: a standard size one inch vidicon tube has only 16 mm of useful imaging area. Therefore 1 inch optics became 16 mm, 1/2 inch optics became 8 mm, etc.
For larger systems the optical format is usually given as rectangular dimensions of the imaging sensor in millimeters, such as 36 x 24 mm in the case of 35 mm film
35 mm film
35 mm film is the film gauge most commonly used for chemical still photography and motion pictures. The name of the gauge refers to the width of the photographic film, which consists of strips 35 millimeters in width...
.
Many image device sheets don't list the actual optical format, but do list the size of their pixels in terms of micrometers, a more helpful equation is to convert the pixel size, and array size, directly to optical format. The equation for this is:
with:
- w = width of array (in pixels)
- h = height of array (in pixels)
- p = pixel size (micrometers)