'''Optical format''' is a hypothetical measurement approximately 50% larger than the true diagonal size of a solid[[Solid-state (electronics)|solid-state]] [[photo sensor]]. The use of the optical format means that a lens used with a particular size sensor will have approximately the same angle of view as if it were to be used with an equivalent-sized [[vidicon|video camera tube]] where(an "old-fashioned" TV camera). In a video camera tube, the diagonal of the actual light-sensitive target iswas smallerabout thantwo-thirds the overalloutside sizediameter, which was the measure used.
The optical format is approximately the diagonal length of the sensor multiplied by 3/2 <ref>http://www.dpreview.com/news/2002/10/7/sensorsizes (table of sensor sizes at bottom)</ref> <!-- To say divided by 16 to give a mm result although approximately valid is not technically correct. It is a bad idea to mix units.---> The result is expressed in inches and is usually (but not always) rounded to a convenient fraction. For instance, a 6.4x4.8&{{nbsp;}}mm sensor has a diagonal of 8.0&{{nbsp;}}mm and therefore an optical format of 8.0*3/2 = 12&{{nbsp;}}mm, which is expressed to the convenient imperial fraction ofas {{1/2}} inch in [[imperial units]]. The reason why it is expressed in inches is historical:, adating standardback [[fourto thirds]]the inch image sensor has a an image area with a diagonalearly measurementdays of approximately {{convert|22|mm|inch}}television. Therefore a 1 inch sensor has approximately a 16 mm diagonal, a 1/2 inch sensor has approximately an 8 mm diagonal, etc.<ref>[http://webcachewww.googleusercontentdpreview.com/search?q=cache:-4HAeseX8Z8J:archive.chipcenter.comnews/analog2002/tn051.htm&cd=1&hl=en&ct=clnk&gl=us10/7/sensorsizes "Digital(table Imagingof Opticalsensor Format",sizes Chipcenter.comat Dec 1, 2000 by Ed Jakl and Mitch Reifel, retrieved Jan 4, 2010]bottom)</ref>{{deadlink}}
Many image device sheets don'tdo not list the actual optical format, but do list the size of their pixels in terms of micrometers,; a more helpful equation iscan be used to convert the pixel size, and array size, directly to optical format. The equation for this is:▼
For larger systems the size is usually given as the true rectangular dimensions of the imaging sensor in millimeters, such as 36 x 24 mm in the case of [[35 mm film]] sized sensors.
▲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:
