Re: ir filter source

[Helmut Faugel TE <htf@xxxxxxxxxx>]

On Wed, 13 Aug 1997, Joseph O'Neil wrote:

> GERMANIUM IR DCX LENS
> Infra Red germanuum double convex lens. 43.2mm diameter, and 5mm thick at the center. 
> Not sure of the focal length.   Shinney surface, will not let visable light pass. 
> Original cost over $1200.00. Unused in original packing..
>        
> 	This item lists for $95 US.  A lot of money to spend on something you are not 
> sure of what use it can be put too.  Has anyone heard of something like this before?  
> Anyone know what it was/can be used for?

AFAIK semiconductors are getting transparent beyond their peak sensitivity
then used as photodiodes. Silicon is getting transparent for wavelenghts
longer than 1.1 um, for Germanium this is about 1.8 to 2.0 um, so this
lens would be useless for 'traditional' IR-photography. 


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