# Optical format

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**Optical format** is a hypothetical measurement approximately 50% larger than the true diagonal size of a [solid-state](/source/Solid-state_(electronics)) [photo sensor](/source/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 [video camera tube](/source/Video_camera_tube) (an "old-fashioned" TV camera). In a video camera tube, the diagonal of the actual light-sensitive target was about two-thirds the outside diameter, which was the measure used.

The optical format is approximately the diagonal length of the sensor multiplied by 3/2. The result is expressed in inches and is usually (but not always) rounded to a convenient fraction. For instance, a 6.4x4.8 mm sensor has a diagonal of 8.0 mm and therefore an optical format of 8.0*3/2 = 12 mm, which is expressed as 1⁄2 inch in [imperial units](/source/Imperial_units). The reason it is expressed in inches is historical, dating back to the early days of television. [1]

Many image device sheets do not list the actual optical format but do list the size of their pixels in terms of micrometers; a helpful equation can be used to convert the pixel size and array size directly to optical format. The equation for this is:

- O F = p w 2 + h 2 16000 {\displaystyle 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)

## See also

- [Image sensor format](/source/Image_sensor_format)

## References

1. **[^](#cite_ref-1)** [http://www.dpreview.com/news/2002/10/7/sensorsizes](http://www.dpreview.com/news/2002/10/7/sensorsizes) (table of sensor sizes at bottom)

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