nominal focal length

nominal focal length

An approximate value of the focal length, rounded off to some standard figure, used for the classification of lenses, mirrors, or cameras.
Dictionary of Military and Associated Terms. US Department of Defense 2005.
References in periodicals archive ?
Tamron has the greatest zooming range of all and the Tamron 16-300mm f/3.5-6.3 Di II ([pounds sterling]430) features a nominal focal length of 16mm at the widest setting (equivalent to 24mm when mounted on a cropped sensor DSLR), and extends out to 300mm.
The scope has a nominal focal length of 650 mm (25.6 inches), but there are optional 0.73x and 0.60x focal reducers that deliver effective focal lengths of 470 mm (f/3.6) and 390 mm (f/3.0), respectively.
For example, a 32 wavelength wide lens aperture would have a nominal focal length of 20 [Lambda], so a normalized path length error of 0.005 would correspond to 0.1 [Lambda], or 36 [degrees] of phase error.
This has tremendous advantages for longer lenses: a telephoto lens with a nominal focal length of 200mm in the 35mm format has a working focal length of 320mm when attached to a digital SLR.
By measuring the difference between these foci, expressed as a percentage of the nominal focal length, we can determine the amount of longitudinal spherical aberration.