Re: Bubbles in lenses (digest 1625)

[P3D Bob Howard <bobh@xxxxxxxxxxxxxxxxxxxx>]

RE: In mentioning Dr. T's wonderful viewer restorations, it was noted 
that some viewer lenses have bubbles in the glass! Was this common is 
asked or what does it mean?

You are not going to believe this reply, BUT once bubble in optical 
lenses were a sign of Quality!!! Of course, if they were too big on 
at a gournd surface the lens element was discareded. If optical 
glass made in big pots was properly anneled to get other qualities, 
sometimes air bubbles were trapped as it cooled. So bubbles were a 
sign of good annealing over time etc. A bubble in a Leica lens caused 
cries of dismay, so the owner was told its only effect was to 
diminish the light by an infinesimal amount and you know you have 
good op[itcal glass etc. In recent years they have learned how to do 
it without bubbles (or don't anneal properly?) take your choice. BobH


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