Optical format

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.^[1]

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:

$OF = \frac {p \sqrt {w^2+h^2}} {16000}$

with:

• w = width of array (in pixels)
• h = height of array (in pixels)
• p = pixel size (micrometers)

External links

• "Image Sensor Size and Field of View" (list of common optical formats at the bottom of the page)

References

1. ^ "Digital Imaging Optical Format", Chipcenter.com Dec 1, 2000 by Ed Jakl and Mitch Reifel, retrieved Jan 4, 2010