LENS DESIGN
 
SECONDARY CURVE WIDTH DETERMINATION

If the lens is a tricurve lens, then the 
width of at least one of the peripheral 
curves must be given.  Typically the 
3rd curve width is specified.  For 
example the TCW may be 0.2 mm wide.  
If the OAD and OZD are known or given, 
which they typically are, then the 
width of the secondary can be 
determined.  The SCW is equal to the 
overall lens diameter (OAD) minus the 
optical zone diameter (OZD) divided 
by 2 minus the TCW.

           OAD-OZD
SCW=  ----------   -  TCW
                 2

For example, if the OAD is 9.4 mm, OZD is 8.0 mm, TCW is 0.2 mm, the SCW would be 0.5 mm.