Purpose
There is a lot of talk on the interweb of radioactive lenses, several youtube videos showing highlighting the fact etc. Since I have a small collection of M42 glass and when I found a cheap Geiger counter I decided to go for it. Note that I don't believe that these lenses are dangerous in any way. Measurements are made 5 cm from the lens, with caps of. Even the plastic cap or doubling of the distance will make significantly lower results. The advice would be not to sleep with the rear element of a radioactive lens 5 cm or less from your eye? Anyway, to the fun part!
Method
I have used a simple instrument for measuring radioactivity that is connected to a smartphone or tablet via the headphone jack. The model is called SMART LAB FSG-001 SMART GEIGER COUNTER and specifications of the sensor are measurement of Gamma X-ray radiation with a measurement error of +/- 15 percent. Added to this is interference from the headphone jack, and that would be different in various devices, so comparison should be made with the same device. My setup was the same during all these tests, and also the device was set to “airplane mode” to not allowing any wireless signals to interfere. Between the device was also a 50 cm extension cord to allow more free movement of the sensor. Not to block any lens elements all lenses was tested with the aperture wide open both for front and back measurements. All test where at least tested for 30 minutes to provide some accuracy and being able to compare between the lenses.
Results
- Super-Multi-Coated TAKUMAR 20mm F4.5 (Rear: 0,81 CPM, Front: 0,28 CPM)
- Super-Multi-Coated TAKUMAR 24mm F4.5 (Rear: 0,19 CPM, Front: 0,27 CPM)
- Super-Multi-Coated TAKUMAR 28mm F3.5 (Rear: 0,26 CPM, Front: 0,25 CPM)
- Super-Takumar 35mm F2 (Rear: 6,71 CPM, Front: 0,23 CPM)
- Super-Multi-Coated TAKUMAR 35mm F3.5 (Rear: 0,11 CPM, Front: 0,33 CPM)
- Super-Multi-Coated TAKUMAR 50mm F1.4 (Rear: 19,73 CPM, Front: 1,52 CPM)
- Super-Multi-Coated MACRO TAKUMAR 50mm F4 (Rear: 0,36 CPM, Front: 0,10 CPM)
- Super-Multi-Coated TAKUMAR 55mm F1.8 (Rear: 13,24 CPM, Front: 0,62 CPM)
- Super-Takumar 55mm F1.8 (Rear: 0,25 CPM, Front: 0,12 CPM)
- Super-Multi-Coated TAKUMAR 135mm F2.5 (Rear: 0,19 CPM, Front: 0,26 CPM)
- Super-Multi-Coated TAKUMAR 135mm F3.5 (Rear: 0,22 CPM, Front: 0,18 CPM)
- Super-Multi-Coated TAKUMAR 200mm F4 (Rear: 0,12 CPM, Front: 0,34 CPM)
- Super-Multi-Coated TAKUMAR 300mm F4 (Rear: 0,16 CPM, Front: 0,24 CPM)
All CPM (Count Per Minute) values larger than one are highlighted yellow. I don't believe that the SMART LAB FSG-001 is an accurate tool for measuring specific values, but since I tested all values for at least 30 min they should be comparable within the results presented here, to say what lenses are more radioactive than other, and in what rough magnitude. What I consider to be radioactive lenses based on these measurements are marked with bold letters. If I get a hold of more old lenses I will add them to the chart! To complete this post why not show a portrait with one of the radioactive lenses :)
Pentax K-01, Super-Multi-Coated TAKUMAR 50mm F1.4 @ F1.4, 1/320s, ISO100
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