Opticallimits

Optically, the biggest problem with bananas is that they are bent, in other words decentered. You first have to straighten them.

without going bananas in the process.

I wouldn't worry about the Lanthanum.

 

It is used in modern optical glass requirigng high refraction UD elements and such.

 

Metabones, who ground their glass in the USA, use it amongst others in their Speed Boosters. I reckon they would only do so if they can adhere to the USA standards, which, as far as I know, are quite rigorous when it comes to radioactivity.

BTW, Metabones are the same guys who design and manufacture special lenses for the police forces (Infrared, UV etc.)

 

Kind regards, Wim

This guy did perform some measurements with a geiger counter - not the Mitakon, but other lenses. It might be useful just to have an idea:

 

https://mbphotox.wordpress.com/2015/07/2...my-lenses/

 

The most active lens he measured is a Fujinon. His conclusion:

 

Quote:For comparison, when you fly from New York to Germany you get a dose equivalent of 0,1 mSv. That’s 10 nights of sleeping with the Fujinon under your pillow.
 

 

 

OTOH, it seems that the radioactive element is always an inner one, so radiation is partially reduced by other glass elements. I'd be a bit worried, though, if I had one of those lenses and I broke it, thus exposing the radioactive element.

  I'm sure theses radiation levels are of little consequence compared to a heavy nights drinking and who has ever worried about that?

 

 ...in fact it's never even crossed my mind!

In fact a radioactive lens element has never been a risk, the only serious risk is some old camera viewfinders that were radioactive, with prolonged daily use the risk of early cataract is increased, although having a cataract isn't considered a disease but just a part of normal aging process, radioactivity (as well as many other factors) just accelerate it, having repetitive x rays or scans, or working at the hospital radiology department increases the risk that's why we have strict precaution measures for radiology employees and that's why they wear special eyeglasses or goggles when exposure is inevitable.

Probably the most annoying fact about some old-fashioned lenses with radioactive elements is that they tend to become yellow. It seems that they can be fixed with a long exposition to UV rays.

Quote:Probably the most annoying fact about some old-fashioned lenses with radioactive elements is that they tend to become yellow. It seems that they can be fixed with a long exposition to UV rays.

That is with glass with thorium oxide in the mix. They become yellow when not used for a long while.

So how are the optics ?