Voigtlaender Apo Lanthar

[Arne Croell]

Thanks Steve! Have you measured (the front lens) whether it is hot? Since you mentioned you have the equipment at hand...
If its not radioactive, that would point to a changeover in the 1966/67/68 time frame.

[Steve Hamley]

Arne,

Neither is radioactive. I was surprised that they weren't.

But I will double check and post the results if I detect anything indicative of added radioactivity. I can also run a gamma spec on it (although I don't see any real reason to), thorium being rather easy to identify.

Steve

[Arne Croell]

Steve, I don't question your measurements. It just wasn't clear to me from the preceding posts, if you had measured already.
That clears up the interesting question when Voigtländer made the change, apparently about 5 years before they stopped production in 1972. Since the production numbers were much lower in their last years, most Apo-Lanthars out there will be radioactive, and only a few are not.

[Steve Hamley]

Arne,

Sorry for the confusion. I'm off today waiting for the cable guy to put in a new internet connection, and checked the lens with my home made geiger counter. Neither cell is radioactive.

Steve

[mhayashi]

Just for two cents, my recent acquisition of Apo Lanthar 30cm with the serial number 7227583, a late 60’s producton shows yellow tint which would indicate the front group is radioactive?? I don’t have a geiger counter, but it seems to contradict to the description of Arne’s Voigtlander paper??
The first picture is after 72 hour exposure to the UV light source.





It turns out a 395nm UVA torch the picture above,

Lepro HD51 Black Light, LED UV Light, 51 LED, High Output Type, UV Light, For Resin, Curing Light, UV Light, 395 nm, 4.5V

isn’t effective enough. I found a page that 370nm is effective, so I decided to buy the 365nm torch made by RichFire. It uses the Nichia Chemical UV LED chip.

5W 3.7V Ultraviolet Flashlight, Nichia Chemical UV LED Flashlight, 365nm Black Mirror UV Flashlight



Notice the single bulb but has a strong light source. The torch is much brighter than the below. Also notice the lens is fluorescent reflection, reacting to the specific wavelength, near 370nm, which I think is also another way to determine whether the lens has the thorium oxide element or not.

The following page is written in Japanese, but can be translated instantly by translation button of the browser or use google translator.

https://voidism.net/blog/

[Bernice Loui]

Very possible yellowing due to thorium glass which was common back when these lenses were made. The yellowing alters color rendition which made these lenses not so desierable back in the day when accurate color balance on color transparancies were a serious consideration.


Bernice

Just for two cents, my recent acquisition of Apo Lanthar 30cm with the serial number 7227583, a late 60’s producton shows yellow tint which would indicate the front group is radioactive?? I don’t have a geiger counter, but it seems to contradict to the description of Arne’s Voigtlander paper??
The first picture is after 72 hour exposure to the UV light source.

[Tom Monego]

Happened on this thread, I have a 150 f4.5 ApoLanthar the SN starts 439xxxxx in a Linhof shutter. The person I bought it from with a Technika IV said he used it professionally in the late 1950s early 1960s. I don't see any yellowing on the front elements, but I am thinking it is probably radioactive. I keep it capped in an old Speed Graphic case. It stays on the Technika as my other lens is Linhof 90 f8 Super Angulon. I am looking into getting a 120 Angulon. What are the percutions I should take with the 150?

[Greg]

What are the percutions I should take with the 150?

Years ago a friend of mine put together the ideal Technika outfit, in his opinion with a 75mm Biogon, 150mm f2.8 optic, 210mm Apo-Lanthar, and a few exotic optics (full set of Luminar lenses comes to mind). Truth be told he was more of a collector than a user. My being able to borrow and use his equipment a few times was much appreciated by me. I did ask him one time if there were any precautions that I should take when using his equipment. He responded with something like "always cap the lenses when not using them, leave cleaning the glass to him, and above all don't drop anything."