The G-Number: A Photometric Lens-Aperture Designation
The photometric aperture or G-number is a more realistic and accurate measure of a lens opening than the relative geometric aperture or f-number. The G-number is the ratio of the field luminance to the focal-plane illuminance. It is a single-number measurable quantity which expresses the exposure effectiveness of a lens opening taking into account all lens and mounting variables. The G-number is easy to measure, explain, use and understand. It relates camera-film exposure to sensitometric exposure, simplifies exposure calculations and the engineering of automatic exposure controlled cameras. The lens efficiency is 1/G.
- Print ISSN
- 0361-4573
- Published
- 1965-02
- Content type
- Original Research
- DOI
- 10.5594/J09265
Download the PDF
or become a SMPTE member today to access the
article.
Become a SMPTE
member today to access the article.