[Leica] Re: Re: FS: Leitz/Leica 350mm f/4.8 Telyt-R

[jcb at visualimpressions.com (JCB)]

At 12:26 AM 2/11/2005, Frank Dernie wrote:


>AFAIK there is no such thing as "APO glass". To get APO performance a 
>combination of elements of differing characteristics and curvature is 
>required to cancel the fact that different colours diffract differently. 
>The unusual partial dispersion glasses which this requires in at least one 
>element are very expensive. Whether the 350 actually has these is 
>debatable. The fact that it is v. sharp is well documented
>Frank



Here's my reference, straight from a lens glass article about Leitz, in 1985:


"Leitz manufactured APO glass at a time when other manufacturers had not 
yet developed the calcium fluoride element."

Then...

"The Leitz APO Glass and the later Nikon ED glass both have similar 
properties, most of which is a closely guarded secret. Leitz has released 
the refractive index of the APO Glass, which, at 1.95, is higher than any 
other glass made today. A Nikon employee once said that given the chance to 
choose, he would choose to use the Leica APO Glass for his own picture 
taking, which is quite an endorsement."

Therefore, my reference to, and I suspect Leitz's reference to, "APO Glass."

The write-up on the 350 says:

"The use of special glasses from the Leitz Glass Research Laboratory and 
the complicated arrangement of the optical components have reduced the 
residual chromatic aberrations in the corners of the picture, usual in long 
focal length lenses, to a level that is no longer disturbing in 
photographic practice. The particularly good detail rendering and the high 
contrast of the 350mm Telyt-R lens also facilitates focusing in poor 
lighting conditions and on rapid action subjects."

I apologize to those that I offended by using the term "APO Glass" but I 
was simply stating both what was said to me by Leitz and what I read about 
Leitz. From what I read, APO Glass was invented by the introduction of the 
calcium fluoride element. A special glass. The special glass (which was 
called APO glass) plus the optical design, produced an APO lens.

JB