Lanthar lenses

[Oren Grad]

You know that trade names come and go nowadays...

Yes. Cosina's use of the licensed Voigtlander names is purely for marketing effect. There is no connection between the optical designs of today's C/V lenses and the historical lens types for which the names were originally used.

[Bernice Loui]

Lanthar was used as a marketing tool for these lenses. They were not the first or the only ones to use Lanthanum optical glass.

"In the early 1930's, G.W. Morey of the Geophysical Laboratory of Washington,
developed some new glasses, and in 1934 came up with a glass with unusual
properties. Eastman Kodak undertook to commercialize this discovery. (For more details of this see Rudolf Kingslake's "A History of the Photographic Lens", p77.) The glasses were referred to as the Lanthanum Crowns. The properties of these glasses are best illustrated by reproducing Kingslake's diagram."

http://www.austincc.edu/photo/pdf/lanthanum.pdf

History of Lanthanum glass is from the USA during the 1930's and commercialized by Eastman Kodak..


Schott cut off the supply of optical glass to the USA during WW-II, so alternatives had to be made and found. Among them were Lanthanum and Thorium optical glass.


What the APO Lanthar offers is wide aperture, good color correction and nice out of focus rendition at large apertures. Stop the lens down to f16 or smaller the differences are less apparent when compared to other lenses of similar design with round a round iris.


Bernice

[mark e mark]

Can someone with the 300mm apo lanthar in a shutter weiht the lens please. I know my camera has difficulties supporting lens over 1000g.

[Arne Croell]

Except that the later APO-Lanthars maybe ended up having no Lanthanum at all. Lanthanum is mildly radiactive and some people would see it risky to walk with one of these lenses in their pocket. I don't know what happened but the facts are these: my APO-Lanthar f4.5 210mm in Compound n.3 is an older lens and produces an easily measurable gamma emission. On the other hand a more recent 150mm in Compur simply does not emit anything measurable. Since the half-life of La 138, the radiactive isotope, is some 60000 years I don't think that it has decayed since the lens was built.

Again, separating La 138 from La 139 (the inert isotope) and using only the latter in the lenses does not look like it can be made on the cheap, so the only reasonable alternative is that Voigtländer at one moment started using some other compound.

But who am I to know...
Tom

Not so. In the natural isotope mix, the stable 139 La has a concentration of 99.9%, and the radioactive 138La makes up the rest. However, 138La has a half life time of 10^11 years which translates to a pretty low level of radioactivity just on its own. At 0.1% concentration, the natural La isotope mix is essentially nonradioactive for all practical purposes. Lanthanum glass is quite alive and available, check out the current Schott glass catalog and see all the glass types with La in the name....
The radioactive Apo-Lanthars used Thorium oxide in addition to Lanthanum oxide in the glass. Voigtländer changed that somewhere between 1964 and 1966 as shown in the 2005 thread mentioned above. Since production numbers were much higher in the early years, the number of radioactive Apo-Lanthars on the market is much higher than that of the nonradioactive ones. More information can be found in my article on Voigtländer LF lenses built after WW II: http://www.arnecroell.com/voigtlaender.pdf