Our equipment varies:
Originally Posted by TheFlyingCamera
- Shutters in cameras have frequently deviated from the stated speed.
- Apertures in lenses have frequently deviated from the stated aperture.
- And then there are light transmission differences due to number of optical groups and the quality of the coatings.
People have frequently applied a different Exposure Index to films, differing from the manufacturer speed. Velvia at EI40 rather than ISO50 is a very commonly known example.
And, meters have always used different values of the Constants within the ISO standard equation for incident meters (constant C) and the equation for reflected light meters (constant K).
- With a hemispherical receptor, ISO 2720(1974) recommends a range for C of 320 to 540 with illuminance in lux. Values typically are between 320 (Minolta) and 340 (Sekonic).
N^2/t = ES/C
- ISO 2720(1974) recommends a range for K of 10.6 to 13.4 with luminance in cd/mē. Two values for are in common use: 12.5 (Canon, Nikon, and Sekonic) and 14 (Minolta, Kenko, and Pentax); the difference between the two values is approximately 1/6 EV.
N^2/t = LS/K
And the above totally does not factor in long standing discussions of reflected meters calibrated for 18% tonality or 13% tonality!
Last edited by wiltw; 06-01-2012 at 06:12 PM. Click to view previous post history.