Common Symbols & Abbreviations

Technical reference information on common optical system symbols and abbreviations.

A Distance from front edge of lens to front focal point
BF Back focal length
C.A. Clear aperture
CT Center thickness
D Distance from back edge of lens to back focal point
DIA Diameter
EFL Equivalent focal length
ET Edge thickness
f/# f-number (focal length ÷ entrance pupil)
FF Front focal length
H Height
H1 First principal point
H2 Second principal point
L Length
nC Index of refraction for red hydrogen C line (0.6563 microns)
nd Index of refraction for yellow helium line (0.5876 microns)
nF Index of refraction for blue hydrogen F line (0.4861 microns)
R1 First radius (moving from left to right)
R2 Second radius (moving from left to right)
R3 Third radius (moving from left to right)
R4 Fourth radius (moving from left to right)
S Object distance
S’ Image distance
V1 First vertex
V2 Second vertex
W Width
    d Abbe constant

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