German and Japanese optical glass

[Erwin Puts <imxputs@knoware.nl>]

Just finished a visit at Leica and Zeiss factories. On the hotly debated 
subject of the relative merits of german and japanese optical glass the 
shared opinion of both factories is as follows:
Optical glass has to be manufactured according to very specific 
parameters and tight tolerances. When these specs are met and the very 
narrow tolerances are obeyed then the glass properties are identical 
irrespective of the origin of the manufacturer. This is as true now as it 
was in 1950.
Some manufacturers produce glass with special properties that another one 
can not make. Then yoy have to buy the product of that specific 
manufacturer. Sometimes several manufacturers produce the same glass. 
Then logistis and price might be instrumental for preferring a certain 
glass. 
If you buy a cheaper glass then the tolerances are by nature larger. You 
have two choices: select that part of the chunk of glass that is within 
specs and throw away the rest: you might end up with the same cost as 
when you had bought the more expensive glass.
Or you use more of the glass and must live with lenses that are not 
within tolerances and then you must decide if this out-of-tolerance glass 
has significant effects on the specified quality of the lens you are 
designing/producing. 
The upshot is simply this: the origin of the glass was and is not at all 
relevant. In the old days Schott could produce a larger spectrum of glass 
qualities and was the preferred manufacturer simply because its glass 
catalogue was larger and their standards of manufacturing quality were 
higher. But the japanese procucers, using the same quality standards were 
able to match Schott and others. 
The optical designers specify the parameters and tolerances and then the 
glass origin is not important as long as these specs are obeyed.
Erwin Puts