[Bob 256]

Only the most sensitive film would have shown fogging over a period of time with these lenses. The radiation is low level and is produced by very small quantities of Thorium in the glass where is is pretty safe in terms of rubbing off or being ingested. The only known issue I've ever heard of from Thorium glass is a danger of accelerating cataract formation when it was used in some eyepieces where the front of the eye would have close exposure for prolonged periods. That was circa 1950 or so. Thorium glass lenses have been known to set off radiation detectors, but one of my watches was pretty capable of that as well (Radium in the paint used on the hands).

There are lengthy discussions of Thorium lenses elsewhere in this forum.

[photoptimist]

I ate a radioactive lens once and have had no side effects.

Well it did make your ears really long and floppy. On the other hand, you look much better with that thick coat of glossy red hair!

[babywriter]

I have a Super-Tak 1.4/50. My wife works in an academic setting, in the sciences, and had the lens emissions measured by a physics technician with a Geiger counter. There was radioactivity, but nothing remotely likely to cause harm.

[TwoUptons]

And mine travelled by air last year with no issues with airport scanners (and it took nice pictures).

Though that was to Canada, where they have enough radiation in the sky that it sometimes glows at night

-Eric

[ffking]

I do know of a couple of Pentax users who mutated into Sony and Nikon users, and I always wondered if it might be because of their old Taks.

[clackers]

I do know of a couple of Pentax users ho mutated into Sony and Nikon users, and I always wondered if it might be because of their old Taks.

(Laughs)

[dcpropilot]

Exposure to this lens at shooting range = 1/4th of a banana
Fukushima Daiichi = 2 Trillion bananas or 200 South Americas

[mccririck]

Is it definitely gamma radiation? I read somewhere else it was alpha. Gamma an travel pretty far through objects unless you block it with a lead sheet.

[photoptimist]

Is it definitely gamma radiation? I read somewhere else it was alpha. Gamma an travel pretty far through objects unless you block it with a lead sheet.

It's all three kinds. Thorium decays into cascade of other radioactive elements that emit various other kinds of radiation of various energies. Each alpha particle emitted by a decaying thorium atom is soon followed by 10 other decays. These lenses grow more radioactive with age although it plateaus at about 10X the original rate after a few decades.

[mccririck]

It's all three kinds. Thorium decays into cascade of other radioactive elements that emit various other kinds of radiation of various energies. Each alpha particle emitted by a decaying thorium atom is soon followed by 10 other decays. These lenses grow more radioactive with age although it plateaus at about 10X the original rate after a few decades.

Ah, so they're probably getting to their most dangerous!

[RICHARD L.]

The radioactive half-life of Thorium is 14 billion years, so don't expect their radioactivity to subside soon ... lol!

Seriously, older 6X7 105 mm f/2.4 lenses were affected by this problem and turned yellow over time. The solution was simply to expose them to brilliant sunlight and the yellow color disappeared.

[moe mountain mike]

i have a radioactive 1:2/55 off a SP500. i has to be over 30 years old with only slight yellowing.
video shows all:
RADIOACTIVE VINTAGE LENS - YouTube

[mccririck]

i have a radioactive 1:2/55 off a SP500. i has to be over 30 years old with only slight yellowing.
video shows all:
RADIOACTIVE VINTAGE LENS - YouTube

lol check this one:

Youtu.be

Youtu.be

[AntonioS]

I did lots of tests with thorium oxide glass in the 1990 decade from Pentax, Olympus and other and the radioactive level is very low.

The Thorium decay is by alpha and the energy is quite low.
The few gamma emission are due to the daughter decays and the energies aren't a problem.

Alpha and beta emissions will not pass a metal shutter curtain and even a cloth one will atenuate reasonably well the beta decay.
I'm not convinced that the total emission would harm a film, unless it stays for years inside the camera and if so, just the frame after the curtain would be affected.
Absolutely no way to damage the film inside the canister or at the winding place.

Bananas and Brazil nuts have more emisssion due to potassium-40 than from thorium glass.

Don't worry with this.



P.S.

It's not just the decay type, but also the half-life and energy emission of each element.
That's the problem when layman people starts to think about some things they don't have a clue of how they work.

Alpha particles would not travel more than a few milimeters in air and will be blocked by a thin paper.
Beta particles may travel up to one meter in air but they are not able to pass through a thin aluminum kitchen foil, glass and plastics
There's no way for the radiation coming from a camera mounted lens to hit the user passing through the camera body or the eyepiece.
Gammas are too sparse to cause any harm
Alpha and beta loose energy as they travel through something like air. Eventually they will hit an atom and for practical purpose, stop.

[mccririck]

Beta particles may travel up to one meter in air but they are not able to pass through a thin aluminum kitchen foil, glass and plastics
There's no way for the radiation coming from a camera mounted lens to hit the user passing through the camera body or the eyepiece.

Hmm, not true, watch the videos above. Beta can travel through a whole book. Unless that's the gammas. From what I've read most betas are stopped by a few milimetres of aluminium, not a sheet of paper.