LENS DESIGN

BLENDS

The junction between the base curve and secondary curve can have a sharp distinction or it can be smoothed out.  If the junction is smoothed out it is said to be blended.  

A tool with a radius between the two 
radii to be blended is used.  This is 
often done because it may improve 
the lens comfort.  

 Blends are usually classified as light, 
medium or heavy.  Sometimes they are 
classified as 1, 2 or 3 or as A, B or C.

 A light blend means that this junction is just slightly blurred whereas with a heavy blend you can not see a junction.