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Re: bubbles





On Fri, 18 Oct 1996, P3D John Bercovitz wrote:

> Allan C. writes:
> > I was wondering if this is just my viewers. 
> Actually, Allan, it's only a problem in your viewers.  You have what we
> call the "Inverse Midas Touch".
> 
> No, seriously, it's a problem with any cemented doublet from that era.
> They're held together with Canada Balsam and the stuff just lets loose
> after a while.  I know of only one way to fix it and it's dangerous.
> Keeping the lens held together, give it a quick little acetone dip.
> The acetone seeps in and reliquifies the Canada Balsam and then leaves
> by evaporation.  It's really dangerous because the whole thing may
> just fall apart on you.  The right way to do it is to soak it in acetone 
> until it comes apart and then re-cement it with a modern cement.  That's
> not something to do at home.
> 
> John B
>  
I can second this advise, as I once used to repair the polarizing filter 
from the Bolex H16 stereo projection lens.  After 40 years, the filter 
material was either degraded or physically separated from the glass elements.
Soaking in acetone (obtainable from most hardware stores) will separate 
the elements, then either use new balsam glue or a newer adhesive from 
Edmund's Scientific.  The trick is to cement the glass elements back 
together without entrapping air bubbles.  If you make a mistake, you must 
immediately resoak the lens before it sets if you use one of the new 
adhesives.  Balsam is more forgiving, but its claimed that it isn't as 
transparent as the newer glues.  Dennis Sherwood   emdesher@xxxxxxxxxxxx  


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