Lanthanum of Old Leica?

[Neugier]

Dear many gentlemen,

Today I got to hear about [Lanthanum] of some old lens.
A sage witnessed it may radiate some extent of radioactivity.
Then I have 2 questions. (I tried search menu in this forum but in vain)
Please let me have a fast sleep tonight. you know someday curiosity tortures.

1. What made the maestro of Leica use Lanthanum in those limited cases?

2. Is it harmful so that really should it be dropped using now?
Does the radioactivity span for ever?

So far, I have experience of some current models and at oldest, 1st gen of Summicron 35.
For me, this new leica myth followed a handmade fluorite legend. so intriguing.

Bests,

Sangmin

[fernando_b]

Lanthanum is a chemical element in the rare earths group, it is NOT radioactive. May be you confuse it with Thorium.
Fernando.

[wizard]

Dear Sangmin,

Fernando is correct, lanthanum is NOT radioactive. It is used in the formulation of glass materials to provide optical glass with a high refractive index. It is quite common still today, but nowadays nobody speaks about it. At the time when Leitz/Leica first used it, in the Fifties of the last century, it was a new development, and so it was mentioned a lot in the literature.

The first batches of the Summicron 50mm collapsible lens, however, did in fact employ optical glass that was slightly radioactive. Later examples employed newly developed different optical glass that had the same optical characteristics without, however, being radioactive.

Sleep well

Andy

[john_r_smith]

According to Richard Nordin, some of the older Zeiss lenses for Hasselblad exhibit quite high radiation levels. Whether they are hazardous to the user is uncertain

John

[jacksparrow]

Shouldn't be that radioactive, otherwise the radiation would ruin the negative! if it glows in the dark... stay away, just like in the Simpson's :-)

[bindrar]

Hi,

Radioactivity can be either as gamma rays, beta rays or alpha particles; the latter two would be stopped by another glass between it and the film (and not cause fogging). Gamma rays would probably cause fogging of film (depending upon the energy of the gamma rays). The glowing is not to to with radioactivity directly, but with another item exhibiting luminescence caused by radioactivity.


And of course I believe that the Lanthanum used is not radioactive.

[albertwang]

Nothing radioactive... just a special glass that's used by Leica.

[xjr]

Lanthanum,I believe,was the NON-RADIACTIVE answer to the Thorium content problem ....

[nemeng]

If you search google you will find an awful lot of silly replies to this question

"It's the Leica Glow!"
"Don't carry them in your trouser pocket!"
"Will it enable me to shoot in the dark?"...

Sigh. Thorium was used as a additive in the 1950s to increase the refractive index of optical glass. As it is slightly radioactive, its use in lenses has resulted in the following:

1. Slight glass yellowing with age.
2. Fretting by 2nd hand lens owners &
3. A seemingly endless amount of flippant remarks in online forums.

See also:

Robert Monaghan's post on Radioactive Glass (Aug 1999):
[Leica] Re: radioactive glass

PhotoNotes.org - Radioactive Glass entry:
PhotoNotes.org Dictionary - Radioactive glass

Use of Thorium in lens glass design:
Thoriated Camera Lens (ca. 1970s)