[ATM] Lens Wedge

[James Gort <jgort@oxford-observatory.org>]

List,

A lot has been written on the importance of reducing wedge in the crown 
and flint blanks of an achromat.  I've searched the web and the ATM 
archives - consensus is that it's important.  And a 'maximum value' is 
usually given.  But no proof.  

I also have a lot books/articles on lens fabrication, ranging from the 
19th century (Brashear, Steinheil, etc.) to modern texts.  I haven't 
found the same emphasis (usually, no mention at all!) on reducing wedge. 

So my question is - does anyone know of an analytical expression for the 
relation of wedge in a lens element to error at the wavefront? Two 
components are at work - the optical path difference (due to more glass 
at one edge) and the angle to the normal of the spherical surface 
(assuming a perfect sphere is slightly tilted with respect to the 
optical axis).

If this has been worked out analytically, can someone please point me to 
the reference?

Thanks!

James Gort

 
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