[Leica] Re: Internal lens filter

[lrzeitlin at optonline.net (Lawrence Zeitlin)]

On Dec 22, 2006, at 9:10 AM, Ed wrote:

> Don't you think an effective approach would be to provide a hot
> mirror layer on one of the optical surfaces *inside* the lenses, at a
> point where the light rays incidence angles are more parallel to the
> axis of the optical system and where internal reflections can be
> optimally minimized?

This is a good idea that goes back more than 50 years. We used to  
insert a gelatin filter between the elements of a lens to warm up the  
excessive blue from early strobe lights. It was also a common  
practice in the movie industry to use a gelatin filter behind turret  
mounted lenses to avoid having to buy a filter for each lens. Many  
professional cine cameras came with a filter slot in the light path.  
Gelatin filters could be obtained in dozens of colors and were thin  
enough not to affect the optical image.

I don't know how they would stand up in temperature extremes or in  
high humidity field work though.

Larry Z