Thorium lenses

[Jerry Attrik]

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Thank you Anbaric.

 

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[sometimesmaybe]

On 11/17/2022 at 11:25 PM, frame-it said:

yes, quite a few lenses actually

i bought a Geiger counter precisely for this reason... i now vet every lens in my collection 😅

[Pyrogallol]

Leica Standard with my 921... Thorium Summicron. Rollei 400 Infrared in Tanol. Copies of darkroom prints made this morning. The infrared film and dark red filter seems to have helped cut through any haze in the older lens.

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[frame-it]

On 11/18/2022 at 1:49 AM, zeitz said:

It is odd that glass sources in Germany, Japan and the US would have the thorium in the glass and then only in a few of their glass products.

thorium is also used in the high resolution camera lenses on the US military Drones

[frame-it]

the lens ive been craving for quite a while and finally found & bought a mint copy last month has quite high radiation,  the images are really nice.

 

[Anbaric]

8 hours ago, frame-it said:

the lens ive been craving for quite a while and finally found & bought a mint copy last month has quite high radiation,  the images are really nice.

That's about a dental X-ray an hour, isn't it? Another lens not to use as a loupe or keep in your trouser pocket!

[nitroplait]

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20 hours ago, frame-it said:

the lens ive been craving for quite a while and finally found & bought a mint copy last month has quite high radiation,  the images are really nice.

I don't know how fast reacting the meter is, but it looks like the readout drastically lowers just a few cm. away from the lens? Did you notice how the fall off was, say 5 or 10cm away?

It could be interesting to measure just behind the camera - where your face is located in a normal shooting situation. I am guessing the shielding of the camera makes it is close to nothing.

11 µSv/h isn't much anyway, unless you sleep with it every night.

You would have to hold it close to a body part for 150 hours to get as much radiation at that spot, as a flight attendant get exposed to from all sides on their hole body over a year. 

[Anbaric]

If it were a point source, the dose reduction would follow the inverse square law - if you started 1cm away, the dose would drop to 1/25 of the original at 5cm, and to 1/100 at 10cm. The lens is a bit big to be considered a point source at these distances, but you should get roughly that reduction. But that's also why using one as a loupe would be bad. You get 100x the 1cm dose at 1mm, right next to a very radiation sensitive organ.