David Krooshof

Radioactive Lenses

I do not feel safe with my radioactive lenses anymore. What now?

[this article will be impropved with more images, video and links, and results of a nikkor 55mm Vasilis gave me]

For my digital color photography (as opposed to digital infrared photography) I used a Mamiya 55mm f1.4 lens as my daily lens. After seeing a lot of photos online, especially on Reddit.com/r/analog I noticed I like Mamiya lenses best. So I got one that I could fit on my GF2, and fell in love with the colors, the sharpness and unsharpness.

For years, this lens was on my GF2, always via a focal reducer optic. That’s an device that mounts to a full frame objective on one end and a smaller camera (m4/3) on the other. Four lens elements in it, bundle the the light from the lens onto the smaller sensor.

I got the lens in 2014, and later learned it was a bit radioactive, especially at the back element. People say not to worry, and I didn’t, also knowing that the lens was always encapsulated in the focal reducer.

Three cameras, the wooden Wista, Mamiya camera, and the Panasonic GF2 with the radioactive Mamiya lens and focal reducer. Behind them is my dog Baloe.

The red one is the Panasonic GF2 with the radioactive Mamiya lens and focal reducer on it.

Why two?

I love that lens. I dropped it, and the internal aperture dial disconnected. Mamiya did not want to repair it, so I got another one, because I know no other lens that is so so sharp yet had such smooth bokeh, that backgrounds are melted to colorful dreamy backdrops. This time, I got a newer copy, that is said was not so radioactive. Later I repaired the first one myself, so then I had two.

When I converted the GF2 for infrared and bought a Sony A7 for the color photography, I moved the newer Mamiya lens to the full frame Sony, sans focal reducer. I felt safe…

How radioactive are these lenses?

I recently made a better case for my geiger counter, and oh dear, that second Mamiya lens is just as radioactive. I can’t put a number on it yet, I have yet to attach my nixie counter display. And even then I cannot see the different energy levels of the detected particles. And the (Russian) counter tube I use can’t detect alpha, only beta and gamma. Thorium is primarily an alpha emitter. All this to say: my tool is rather crude. This article, however has numbers about them, along with a very detailed description, but oddly does not mention their radioactivity as a con. Most folks on the internet echo that the lenses are safe to use, because you need think that to feel safe using these great lenses.

To put the radiation in perspective: there is a photo online of a package with this lens in it, that was rejected by a postal service for being too radioactive. I do not feel safe enough using it daily after I saw that.

Photo of a parcel with stickers saying that it was rejected because the level of radiation was unacceptable. Imagine being the postman that has to return this parcel.

Imagine being the postman that has to return this parcel. (Image links to the source.)

Thorium is an alpha radiator. My geiger tube can only see beta and gamma. Why can I still detect the radioactivity?

A white backround with a diagram on it, consisting of colorful balls.

Because further down the line, there is also Beta- radiation in the decay chain.

So… I am looking for a new old lens.

I have a peculiar taste for unsharpness, I do not want swirls nor soap bubbles, but watercolors. And I want the lens to mount on the fabulous Arax tilt adapter. The need for a tilt adapter limits the choices to m42 and Nikon F mount objectives. There is a modern Chinese tilt lens, but it is simply not sharp. There are a few other options, like the tilt macro from Asthori, but that’s an 85mm. And upgrading to a fujifilm mediumformat wit the new 110mm tilt shift lens, is something I can’t afford.

And down a rabbit hole I went: So many old lenses to consider. There is a Nikkor 50mm f1.4 lens based on the same design as the Mamiya 55mm f1.4, by the same person, but it’s corners are already dark, so there no room for tilt; whole edges would get dark. Tilt requires a bigger projection than the sensor is. I noticed the same issue with the Nikkor 50mm f1.2, it’s coverage is too small to allow for tilt. That’s a bit counter intuitive given the huge size of the exit pupil of that lens.

Coverage is a lens specification that is readily available for large format lenses, and oddly also for Mamiya RB/RZ lenses, but nobody seems to have kept such data for 36x24mm frame Nikkor and M42 lenses. Looking at images taken with lenses does not help, because people often add or remove vignettes. So buying a lens that allows for tilt, is a gamble.

Same for radioactivity. There are lists, correct and false information, and debates. For many good old lenses, it is unclear if they are radioactive, because many people are just saying things. Sovjet lenses are often on the lists, though most are okay. Maybe it’s a cold war assumption, to think all things Sovjet are a nuclear threat? For instance, none of the Sovjet Helios 44 variants are radioactive, while most of the Takumars are. The really good German and Japanese M42 lenses have very often are, because they apply radioactive thorium crystal glass, allows for lens designs with less chromatic aberrations, and wider apertures. For instance, there is Takumar f2.4 heliar type lens that is not radioactive, but of the faster f1.4 type, only the first type is not radioactive. And with my own experience with my two Mamiya 55mm lenses, claims that a lens is not radioactive, is also a bit of a gamble. Especially knowing that my taste strongly favors thorium glass, I should be careful what I choose next.

Screenshot of eBay. The lens has mold. The seller claims "excellent plus plus".

Another issue with buying Japanese lenses online, is that Japanese call most things "excellent" and "exc++" should be understood as just 2 on a five point scale of excellency, meaning that something is off. In this case: notice the mold in the bright spot in the lens.


So, I decided that I should try a Zenitar 50mm f1.7. Not as fast as the Mamiya, and a bit wider angle. The reports about it’s radioactivity vary. If it is radioactive, then according to internet rumors, it is not thorium glass but lanthanum, which is a far less radioactive metal to make crystal glass with. So I ordered one…

It turns out my copy does not radiate any beta or gamma above the background level, which is a good indicator that there is no radioactive decay chain reaction happening at all. So that is a relief.

The bokeh is smooth, which makes it hover behind the subject, rather in the same plane; which is what I want, what I really really want. Sharpness is good enough.

I rotated the distance number ring to make sure the infinity end stop is where the horizon is in focus, and the numbers are correct for the setting of the focus. Not every lens allows tube this. Colors are a bit less saturated, which I could easily compensate in the camera.

The best thing about the Zenitar 50mm f1.7 (by KMZ), is that the projected image circle is so big that even focused at infinity + wide open + full tilt, there is no vignetting to speak off.

So let’s see how this lens behaves in my hands in the near future. I might have found my new, safe, daily shooter.

My hand holding a Sony camera, with a Sovjet lens on it. Zenitar is spelled in Cyrillic. The lens it tilted a bit to the left.

A new to me Zenitar lens on an Arax tilt adapter

Takumar 50mm f1.4

Found the early 8 elements version on the local marketplace. Much to the surprise of the kind seller (Maurice), I tested it for radioactivity.

This is the only variant of that lens that isn't, all the later versions are. The location of the infrared indicator is the main method of telling them apart. If it is near the f2.8 indication, it is quiet. But if the red stripe is near the f5.6 indicator, it is the radioactive thorium glass variant.

For a lens that is about 5 years older than I am, it is pristine condition.

I just learned this verions has fairy dust bokeh, as one photographer called it. The super multi coated lenses have better flair control though.

Some people on the internet say that the coatings are what is radioactive about lenses. That is not true. It is the glass. Coatings are a way of controlling flairs as well as abberations, and the control over coatings is what made it possible to make modern fast lenses perform very good without thorium glass.

To add: Micro-Nikkor 55mm f3.5

For me, the difference between f1.7 and f1.4, simpy means a shorter shutter time at night. And this is also why wide open sharpness is important to me.

There is however an upshot to a so called slower lens (meaning a lens that has a smaller aperture, which causes longer shutter times).

When you stop down a f1.4 lens to f4, several things happen: light bounces around in the lens. Especially infrared light does that, resulting in a blue center of the image. Also, the blades edges and corners start to diffract light. Edges do that, which is why pinhole cameras never produce very sharp images. And the shape of the aperture becomes the shape that is repeated in the unsharpness. So unless a lens has many aperture blades, the unsharpness of a f1.4 lens at f4 is is bound to become restless, while a lens that is f3.5 wide open, will render the out of focus backdrop smoother.

So for scenes that need a recognizable background, a slower lens is better.

One could guess that a macro lens is not tuned for corner sharpness at infinity, but this micro-Nikkor very much is.

Conclusions, so far

That’s a lot of text. But all of this nerdy business is just to get the dangers, the distractions and even the tech out of the way enough to make art in an intuitive way, rather than being ratioactive.

What is left is the ethical question: is it morally okay to sell or give away the Mamiya lenses? Their value is similar to other lenses of the time: 75 to 180 common money units. The information about their radioactive radiation might get lost easier than it took me to acquire. I might hand them in as nuclear waste.

Zenitar 50mm f1.7 photos

Photo of a dude with long grey hair (me) in a forest (natural habitat)

The bokeh is not swirly, like the Helios lenses do, and have no edges like soapbubbles.

Spiderweb connected to a wooden pole and some barbed wire.

Tilt allowed me to run the focus in the horizontal plane along with the spiderweb, and this didnot cause vignetting at the top.

Lots of green with a tiny brown dragonfly in the middle sitting on barbed wire

factor 2 zoom. A good indicator of the sharpness wide open and the depth of field.

Photo of a guy with a blue hat, in front of a blurry background. This background expresses our conversation to a certain extend.

Not a testshot, but actual usage of the Zenitar lens: My valued coworker, choreographer and teacher Melvin Fraenk. Wide open, very slight tilt applied.

Takumar 50mm f1.4 photos

Close up photo of a dark haired guy eating. His hand is in the frame, but it is out of focus, as is the hospital background. The guy is smiling hard.

I could go on about lenses, but with this one, I feel it is about the person again.

buste portrait of a cat with no hair, except on the nose, looking up.

Valente at f4