Common 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
vd = Abbe constant
