Radioactive lenses

Started May 20, 2012 | Discussions thread
ProfHankD Veteran Member • Posts: 5,214
Re: Radioactive lenses

Carlgo wrote:

The whole idea of a radioactive lens with some weird glowing color is very interesting.

As others have said, they don't glow but often yellow. The yellowing seems to change the optical properties somewhat, not just tint, so it is worthwhile to try UV light bleaching.

What are the real-world advantages, if any, the dangers, which ones are to die for (so to say). Any info appreciated.

Except for some military lenses, the radioactivity levels are generally believed to be farily harmless -- significantly less hot than red fiestaware, and you don't eat off your lenses. Some idiot has a video posted of "fixing" a yellow lens by smashing it with sledge hammer -- DO NOT DO THAT! The only way these become truly dangerous is if you get the radioactive material into your body, and few methods would be as effective as inhaling particles from a smashed lens.

There is some debate as to what radiation is emitted by these lenses. Basically, the primary radioactive material is not very dangerous (and not a gamma emitter), but some of the daughter products are more energetic. The radioactivity wasn't put there deliberately, it is just different isotopes and trace contaminants in the materials used to change the glass properties, so there can be a significant difference in radioactivity from one lens to another even of the same model.

The special optical properties these materials gave glass served much the same purpose in older lenses that cheap aspherics do now. Many of the lenses with radioactive elements were smaller, needed fewer elements to correct aberrations, and/or were optically better than those without them. Keep in mind that minimizing element counts made a huge difference with older coatings.

Outstanding radioactive lenses include:

  • M42 Pentax Takumar 50mm f/1.4. One of the best bokeh lenses and exceptionally compact. Definitely shows degraded sharpness if yellowed, but responds well to UV cleaning.

  • Minolta Rokkor 58mm f/1.2. I don't have one (too pricey), but these are apparently outstanding optics with classic radioactive yellowing.

  • Minolta Rokkor SI 28mm f/2.5. Absolutely top IQ, even wide open, but the radioactive element is deep inside the lens where UV has trouble getting to it. IQ gets mediocre if yellowed, but it can take a very long time to UV clean -- weeks rather than hours.

  • Some of the SSC lenses from Canon are particularly hot, especially the 50mm f/1.2 and 35mm f/2 (concave front element). I don't have these, so I cannot say how necessary or effective UV cleaning is.

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