Lantharium coating ??

[fredus]

Hi there,

 

I'm shopping for a 50mm summicron collapsible when I've found this

auction: <a

href="http://cgi.ebay.com/LEICA-SUMMICRON-50MM-F2-COLLAPSIBLE-M-LENS-LANTHARIUM_W0QQitemZ7580561132QQcategoryZ29965QQssPageNameZWDVWQQrdZ1QQcmdZViewItem">HERE</a>

... What the hell is Lantharium coating ? Can't find any info about it ...

 

Thanks for your help !!

 

Fred

[bert_keuken2]

Lanthane glass more likely. Search for "radioactive" Leica glass...

[keirst]

It's a misspelling. It should be "lanthanum", the rare earth element, atomic # 57 in the

periodic table. See: http://www.webelements.com/webelements/elements/text/La/key.html .

This lens used lanthanum crown glass for improved performance, but many 50mm

Summicrons have this.

[vivek iyer]

Lanthanum glass (Not Lantharium or Lanthane).

 

Lanthanum is one of the rare earth elements. Its oxide is used to make glass with different optical properties.

 

Lanthanum by itself is not radio active.

[bobatkins]

Lanthanum.

 

Lanthanum Fluoride has been used in anti-reflection coatings for lenses, just like Magnesium Fluoride and other materials of similar refractive index and durability. Nothing particuarly special about Lanthanum in this context.

[mark-j]

Fred: I had a LTM collapsible Summicron dating from 1951 that had this construction. The lens had a yellow cast to it when comparing it to other lenses. When shooting with slide film, the photos were very warm compared to ones from other Leica lenses. I thought it was LANTHANUM. The front element coating is very soft.

 

Mark J.

[fredus]

Thanks folks. I wasn't familiar with this ... Looks like this is nothing special then ...

[alex_lofquist]

I wonder if the addition of lanthanum to glass would make it shrink? Have you heard of the lanthanide contraction?

[dan_fromm2]

Lantharium? Its in the same column in the periodic table as Unobtainium.

[vivek iyer]

Alex, You old timer! A good one (sort of an 'insider' Chemist geek joke)!

 

Dan, Unobtainium?! Everything has its price :-)

[nathaniel_pearson]

A series of rarified, if not really earthy, jokes flying around here.

I thought maybe a lantharium was an ancient Roman lens foundry.

[dan_fromm2]

Hmmm. Wasn't Lantharium glass used in the Apo-Lancet lens?

[john_shriver]

Production Summicrons used LaK9 glass, which is a nominally Thorium-free Lanthanum glass. But the refining techniques were less than perfect originally, and there was some Thorium. All Thorium is radioactive, although mildly.

 

The alpha particles from the decay of the Thorium cause the yellowing of the glass. Strong sunlight (UV?) will clear the yellowing. If you don't clear the yellowing, the results are obvious with color film.

 

Now, some of the prototype Summicrons may have used an intentionally Thorium bearing glass. But they look like Summitars, and I think they are labeled "Summitar*". Those prototypes are rare.

[vivek iyer]

Does anyone knows why/how UV *cures* the yellowing?

[adrian bastin]

Sellers on thebay often make out that the early Summicrons, below No. 1000000, are rare and sought after. And they usually get the spelling wrong on Lanthanum (hope I got that right) which all these early 'crons have. I have one of these yellow ones, No. 1021xxx ; much prefer, and use, the slightly later one.

 

Adrian

[david k.]

I'm impressed, what other camera specific forum, would provide this level of answers, to a question like this :)

[bob in seattle]

The LanthOFlex site, now defunct.

 

By the way, the Lantharium was where Romans who spoke Castilian Spanish, as well as some Ladino-speaking Sephardic Jews, kept their lances when away on holiday...

 

Bob in Seattle (23 days of rain and counting...record is 33 days...great market for 400/800/1600/3200 film these days...)

[adrian bastin]

Fred

 

I just took a look at the link you provided to the auction. And there is the wonderful spactacle of a seller shooting himself in the foot with claims of rarety. It's very unlikely this M lens has lanthanum anything - and who wants a yellowing lens, anyway.

 

Adrian.

[duane_kucheran]

To Vivek,

 

Sufficiently strong UV will bleach out most any dye or coloring. That's why most colored stuff fades after a while in the sun. One optical device I worked on had a continuous Xenon arc lamp (not the flashed type) that was a great UV source. The black anodized lamp housing's interior coating turned clear after about a year.

 

I don't know if solar UV is strong enough to do that, but I hear tell that UV levels have increased over the past few years due to ozone depletion...

 

Cheers,

[alan_clayton]

...anium & ...erium and other things that glow in the dark ...

 

"Apparently" when 3 Mile Island reactor building was being cleaned up after that 'small leak' the radioactive contamination would be successfully removed one day only to re-appear the next. The elements involved were thought to be new to the periodic table and christened Disappearium and Reappearium. A bit like the coatings on 1950s Leica lenses that some dealers claim are there but I can't see!

[vivek iyer]

Duane,

 

It is getting too complicated for the all of us. Thanks for your post. I know the mechanisms by which organic dyes get bleached (excitation by UV and bleachning by chemical rearrangements and or by oxdidation by atmospheric oxygen).

 

I am perplexed by the coloring in glass and its bleaching which I think is different.

 

Thanks again!

[dan_fromm2]

Vivek, I think that Michael Briggs explained the phenomenon at his site http://home.earthlink.net/~michaelbriggs/aeroektar/aeroektar.html

 

To paraphrase badly, gamma radiation from the Thorium and decay products knocks electrons loose, creating "color centers." A UV photon adds enough energy to a misplaced electron to allow it to move from the potential wells ists trapped in back to its normal position. And so it goes.

 

Cheers,

[vivek iyer]

Dan,

 

Thanks for supplying Michael Briggs' fabulous page for all of us.

The most informative on this topic anywhere!

 

I am still in the dark about the bleaching process.

[eliot_rosen1]

John is right. The yellowish color of the glass in some of the early 50/2 collapsible Summicrons (mostly those with serial numbers of 104xxxx and earlier, but a few with later SNs) is due to use of batches of lanthanum glass that had radioactive thorium in it. The coating of these lenses was the typical blue coating used by Leica in the 1950s: it was the glass not the coating that was yellow.

 

The amount of radioactive thorium varied from batch to batch of the glass, so you can find lenses with different degrees of yellow coloration. The levels of radioactivity are said to be low, but I would still avoid holding the lens up close to my eye. [Just as a precaution. :-)]

 

I think the blue coating somewhat balances out the yellow color of the glass, so these lenses do not give somewhat cool color rendition that a number of the early leitz postwar lenses give.