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Radioactive Lenses and Every thing About Them


There’s a variety of misinformation about radioactive lenses – from scare tales about rising an additional arm and getting most cancers, all the best way to saying that radioactive lenses are totally innocent. The reality is someplace between the 2 extremes and requires cautious consideration. In any case, these lenses include radioactive substances, and we should always deal with them with some care.

Such as you, I wished to be protected and perceive tips on how to take care of the radioactive lenses. I had so many questions: Learn how to deal with them? What harm might they do to me or the digicam? Or possibly, I ought to give them away to an individual from the discussion board providing to “take them away from me” to save lots of me from hurt? (Good attempt, buddy!)

After studying numerous articles, research, and books, I’ve compiled the solutions to the most typical questions.

Well being Physics Poster from Oak Ridge Nationwide Laboratory (1947)

Disclaimer: This text is solely informational, and mustn’t by no means be used as medical, well being, radiation safety, or security recommendation, implied or not.

What Makes Classic Lenses Radioactive?

Thorium and lanthanum, primarily. Digital camera lenses include optical glass made with varied uncommon parts like lead, boron, calcium, lanthanum, and thorium dioxide. These parts have distinct optical properties, permitting producers to create lenses of superior high quality.

Each lanthanum and thorium dioxide are radioactive, though radioactivity from lanthanum is so small that it isn’t detectable with out delicate lab gear. Lanthanum is barely weakly radioactive as a result of solely 0.089% of it’s lanthanum-138, a radioactive isotope and the remaining 99.9% is non-radioactive lanthanum-139.

Unique parts corresponding to Thorium, Lanthanum and Zirconium are added to glass mixtures to create the excessive refractive indexes crucial in subtle lens designs. Choice of premium portions of glass from the massive glass pots, stringent spectrophotometric checks after stress and pressure checks present the dear uncooked glass for final use in lens parts. —Konica Hexanon Lens Information, Konica Digital camera Firm, 1972

Historical past of Radioactive Lenses

In 1945, Paul F. De Paolis, from Eastman Kodak Firm, filed a United States Patent 2,466,392 for Optical Glass, which launched thorium and optical glass making properties.

This utility pertains to glass having optical values in a variety that’s helpful for the designing of optical devices. Particularly, this utility pertains to such glass having an index of refraction for the D line (n) within the vary between 1.65 and 1.68 and an Abbe worth (v) between 52.5 and 57.0.

Basically, the glasses herein described are non-silicate and embody because the glassifier boric oxide in an quantity between 35 and 40 % by weight; lanthanum and thorium oxides in considerably equal quantities, higher than ten %, of every; and barium oxide and both calcium or magnesium oxide. —United States Patent 2,466,392.

Kodak produced a few of the first radioactive lenses for aerial surveillance – the Aero-Ektar. Different producers like Canon, Konica, Asahi Pentax, and others additionally used thorium of their lenses made between about 1945 and 1980.

Producers largely used thoriated glass for the quickest, dearer lenses, such because the f/1.2s and f/1.4s, however slower radioactive lenses additionally exist.

Ultimately, by the early Eighties, the thoriated glass fell out of use for shopper lenses – because of the manufacturing facility employees’ well being issues and shopper radiophobia following nuclear accidents. Newer formulations appeared, providing related properties with out the added threat of radioactivity.

Optical Properties of Thoriated Lenses

The addition of thorium oxide, or thoria, to the glass will increase the refractive index whereas sustaining low dispersion. These properties are particularly useful for making optical glass.

A excessive index of refraction means gentle travels slower throughout the glass, and subsequently, adjustments its path extra simply. Lenses can have a decrease profile, require much less materials and thus be lighter.

Low dispersion, outlined by Abbe quantity, permits lenses to appropriate chromatic aberration, making certain the identical focus is maintained all through the entire vary of colours within the seen spectrum, creating sharper pictures.

Combining these properties permits for lenses with wonderful optical efficiency.

What’s Thorium?

Thorium is a weakly radioactive metallic chemical component with the image Th and atomic quantity 90. All recognized thorium isotopes are unstable. Essentially the most steady isotope, 232Th, has a half-life of 14.05 billion years, or concerning the age of the universe. It decays very slowly by way of alpha decay, beginning a decay chain named the thorium collection that ends at steady 208Pb. —Wikipedia

Thorium is a naturally occurring, most considerable radioactive component within the earth’s crust. Thorium is comparatively steady and has a half-life of 14 billion years.

Do Radioactive Lenses Emit Solely Alpha Particles?

Probably not. Whereas it’s true that pure thorium decays by emitting an alpha particle as acknowledged above, that is solely the beginning of the lengthy collection of decays that emit alpha, beta, and gamma radiation till it ends with the steady isotope of lead. You possibly can learn it as such:

Thorium 232 -> releases alpha α -> turns into Radium 228, then
Radium 228 -> releases beta β- -> turns into Actinium 228, and so forth.

Picture by BatesIsBack / Wikimedia Commons and licensed beneath CC BY-SA 3.0.

The above decay chain demonstrates that thoriated lenses include thorium and its daughter parts: radium, actinium, radon, polonium, bismuth, thallium, and lead in minute portions, ensuing from sluggish thorium decay.

What Is Bremsstrahlung Radiation?

When beta particles decelerate inside denser supplies, such because the barrel surrounding the lens, they create electromagnetic radiation by releasing a photon – an x-ray or gamma-ray. This secondary radiation is known as “bremsstrahlung, German for “braking radiation”.

Most classic lens barrels are metal, copper, or aluminum and produce tiny quantities of secondary gamma radiation. The heavier the shielding materials, the extra bremsstrahlung radiation is emitted.

Attributable to how little beta decay there may be, the ensuing bremsstrahlung radiation can also be minimal. Nonetheless, it’s value mentioning for completeness to know what kinds of radiation you might count on from a lens.

Risks of Radioactive Lenses

Glass mud and high quality particles

Parts within the thorium decay chain are extremely poisonous and harmful on their very own and in bigger portions. Nonetheless, the quantities current within the lenses are tiny and solely exist for a short while.

Breaking the lens won’t “launch” the radiation or the poisonous parts which stay within the glass lattice construction. Nonetheless, it is going to contaminate the premises and make it simpler to ingest or inhale small bits of radioactive mud.

Alpha particles can solely penetrate a number of micrometers of the outer layers of human pores and skin and are innocent – so long as they’re outdoors the physique.

Alpha-emitting particles are considerably extra harmful contained in the physique. Ionizing properties of the alpha particles trigger harm when they’re near the cells — particularly, these within the respiratory tract and lungs and the digestive tract, abdomen, and intestines.

Guarantee you don’t smash, grind, scratch, or scrape the lens parts to keep away from getting radioactive particles contained in the physique. As a superb measure, I additionally wash my fingers after dealing with them.

Well being Physics Poster from Oak Ridge Nationwide Laboratory (1947)

Eye harm from radioactive lenses

For makes use of of thoriated optical glass which are approved beneath this exemption, the lens can be enclosed by different supplies or there can be further materials between the lens and the tissues of an uncovered particular person, and solely photon exposures can be of concern. Nonetheless, in unauthorized makes use of of thoriated optical glass, corresponding to eyepieces of optical devices, publicity to the attention to alpha and beta particles additionally can be of concern. This concern is due to the proximity of the glass to the attention and lack of adequate absorbing materials between the supply and tissues of the attention. —nrc.gov NUREG-1717 Web page 3–288

Elevated radiation publicity can trigger cataracts within the eyes, subsequently keep away from needlessly exposing your eyes – put on glasses and don’t put radioactive lenses near the bare eye when cleansing or dealing with them.

Robert C. McMillan & Steven A. Horne – Eye publicity from a thoriated optical glass – irpa.web

Testing confirmed that easy eyeglasses successfully protect radiation emitted from the lens – solely one-tenth of the radiation will get by way of. I measured roughly 3006 CPM by way of glasses versus roughly 28000 CPM on the floor.

Again of a Konica Hexanon AR 57mm f/1.2 exhibiting 27847 CPM of radiation on the floor
A radioactive lens with easy glasses
Measurement exhibits a big drop of radiation when glasses are positioned between the lens and the counter

Radiation publicity from radioactive lenses

In response to the analysis (under), radioactive lenses are comparatively protected. We’re often uncovered to radiation from varied sources on daily basis, which mixed give a extra vital dose than using radioactive lenses would:

  • Strolling round outdoors within the solar (important contribution to the annual radiation dose)
  • Staying at house (Radon from the constructing supplies, tiles)
  • Consuming bananas (Incorporates potassium-40)
  • Consuming brazil nuts (Incorporates Radium-226)
  • Flying on an aeroplane (about 2μSv/h of Cosmic radiation)
  • Getting an x-ray on the physician
  • Sleeping subsequent to somebody (the opposite individual is radioactive to us (potassium-40)
  • Having a smoke detector (incorporates americium-241)
  • Having a granite countertop (uranium and decay merchandise)
  • Smoking (releases radium, lead-210, polonium-210)

The overall gamma vitality launched each second from the Carl Zeiss Tessar, however, was nearly 32 MeV/s. The contribution from this for a photographer to the utmost annual dose to the entire physique was calculated to be simply 0.17 ‰. That is similar to the elevated dose from beta radiation. Thereby the beta and gamma radiation from the Carl Zeiss Tessar are equally non-hazardous. These ratios are so near zero that the conclusion drawn on this thesis is that there are not any radiation-related well being hazards concerned within the utilization of any of the digicam lenses measured. —An Evaluation of Residual Radiation in Thoriated Digital camera Lenses. Jonathan Wäng and Viktor Henningsson, 2013.

Learn how to Determine Radioactive Lenses?

Essentially the most dependable option to decide whether or not the lens is radioactive is by measuring it with a Geiger counter. Nonetheless, few folks have easy accessibility to at least one, and in that case, a visible inspection could possibly be used as a backup.

Visible inspection can reveal hints that the lens is radioactive – radiation over time causes yellowing of the lens parts. Nonetheless, growing old, in addition to the composition of the glass, can even trigger discoloration of the glass.

Wanting by way of the lens at a white sheet of paper reveals the weather’ yellowing in comparison with the encompassing white paper. A big distinction in tone signifies a better probability that the lens is radioactive. However, clear glass doesn’t imply that the lens doesn’t include radioactive supplies – it could go each methods. Radioactive lenses lose their yellow tint when uncovered to UV gentle.

Utilizing a white background to see the yellowing of the lens. Hexanon AR 57mm f/1.2 is radioactive, whereas the Hexanon AR 35mm f2 will not be radioactive. It’s evident that the AR 35mm is whiter.
Canon FL 58mm f/1.2 clearly exhibiting off its yellow parts

Is Lens Coating Radioactive?

Lens coatings are available quite a lot of colours, which can seem yellow when seen from an angle. The coating colour will not be associated to lens radioactivity and could be of any colour for radioactive, and non-radioactive lenses.

Some sources incorrectly state that the lens coatings are radioactive – that isn’t the case. The precise glass incorporates thorium – not the coatings. For instance, Mamiya makes use of yellowish coatings on most of their classic lenses, whereas solely a few of these lenses are radioactive.

Why Do Radioactive Lenses Yellow Over Time?

Radiation creates F-centers within the glass as a result of radioactive decay displaces electrons, which trigger the glass to take a yellow or brown tint.

UV gentle can clear a few of the yellowing. It might take as much as 7 days of publicity to the solar, or UV gentle sources to minimize the yellowing. Nonetheless, I like the nice and cozy colour solid in my photographs, and go away the lenses as they’re – it’s a distinctive “characteristic” of a thoriated lens.

Learn how to Retailer Radioactive Lenses?

To keep away from elevated radiation publicity – retailer the radioactive lenses as distant from your self as moderately doable. If in case you have a alternative, don’t hold them within the bed room or places the place they’re near people for extended durations. Regardless that the exposures are small, all of them add up over time.

I measured a drop of radiation readings to background ranges at about 1-1.5 meters away from the lenses.

An aluminum case is an efficient choice as a result of it’s a good shielding materials for alphas and betas. Nonetheless, storage container materials doesn’t make as a lot of a distinction within the dose charges as distance, so in case you are anxious – improve the gap between your self and the lenses.

At a distance of about 45 cm from three radioactive lenses pointing at detector I get 236 CPM
Similar distance, however with lens caps or UV filters on the extent drops to 86 CPM – about twice the background degree.

Measurement Tools

I measure my lenses utilizing GQ GMC 600+ and GQ GMC 300E+ Geiger-Muller counters. GQ GMC 300E+ makes use of a extra widespread M4011 GM tube, which isn’t very delicate to Alpha radiation however detects Beta and Gamma. In the meantime, the GMC 600+ makes use of LND 7317 pancake GM tube and may be very delicate to all kinds of radiation.

Do Radioactive Lenses Injury Cameras?

All electronics are inclined to radiation harm to a point – digital cameras endure from the formation of scorching pixels on the sensor.

A easy check exhibits how radiation may have an effect on the digicam sensor. After 90 seconds of publicity with a lens cap, a radioactive lens left seen “excited pixels” within the picture. That’s the place the high-intensity particles hit the sensor. The pixels returned to regular for the following body, and weren’t “caught”, however I believe it’s a good suggestion to take away radioactive lenses from the digicam physique and be on the protected aspect.

Extra details about scorching pixels could be discovered on Hubble telescope digicam, CMOS picture sensors, and Reddit.

Posting Radioactive Lenses

Radioactive lenses don’t often trigger issues for posting. I had varied lenses shipped with none bother, besides from one time, when a Mamiya Sekor 55mm f/1.4 was being shipped from the USA utilizing the eBay World Transport program. World Transport despatched the lens again to the vendor with a notice stating that radioactive supplies should not permitted.

Parcel rejected when sending a Mamiya Sekor 55mm f/1.4

Are Radioactive Lenses Nonetheless Being Made?

Present shopper lenses don’t include thorium – it has been changed with newer formulations of glass, avoiding the radioactivity downside. The primary concern was the manufacturing facility employees’ well being – no one would need to polish and grind the glass and expose themselves to radiation. Additionally, folks’s worry of radiation makes the completed product difficult to promote.

Curiously, thorium continues to be utilized by the USA navy, within the state-of-the-art World Hawk drones.

On June 21, 2017, a U.S. Air Power RQ-4 World Hawk crashed close to Mt. Whitney, which lies on the boundary between Sequoia Nationwide Park and the Inyo Nationwide Forest in California. It’s rugged, closely forested terrain, and now the service needs somebody to go in there and recuperate components of the drone.”

“Thorium is a radioactive materials and decays by way of alpha emission. If the lens has been burned or it has been melted the potential for alpha radiation publicity is larger. —TheDrive

The plane additionally has an optical lens which is impregnated with Thorium to boost optical properties (much like many business optics) —The contract doc

If the USA navy chooses to make use of thorium to energy their drone optics, maybe we will say that it’s nonetheless the most effective glass when absolute high quality is required?

Are Radioactive Lenses Higher?

A number of the most wonderful classic lenses ever made are radioactive. Is thorium to “blame” for his or her success, or is that this solely a coincidence? Tough to say, however the truth that thoriated lenses are utilized in top-quality optical methods of navy drones suggests the previous.

I examined fairly a number of radioactive lenses and fell in love with them. The Mamiya 58mm f/1.7 exhibits distinctive optical efficiency – pictures are sharp and contrasty with placing heat color.

I’m but to search out an optically poor instance of a radioactive lens – fairly the opposite – they’re all wonderful.

Fashionable non-radioactive lenses surpass these classic lenses in absolute sharpness and distinction. Moreover, they often characteristic extra advanced designs, with extra parts and teams. Nonetheless, the optical properties of the classic lenses are extra pleasing to some folks – together with me.


In regards to the creator: Mantas Kalausis is the photographer behind the web site Lens Legend, an internet site about classic and trendy lenses with every thing from pattern photographs to opinions. The opinions expressed on this article are solely these of the creator. You’ll find extra of Kalausis’ work on his web site, Fb, Twitter, and Instagram. This text was additionally printed right here.



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