[cdd29]

In short, what is the draw to some of the older throuim glass lenses? Are they that superior in IQ or just the novelty of being a little on the radioactive side?

[Alex645]

Thorium oxide helped to improve the refractive quality of the glass. Yes, compared to similarly priced lenses at that time, they had superior IQ.

[stevebrot]

In short, what is the draw to some of the older throuim glass lenses?

Nothing to do with the thorium. I don't know of any thoriated lens that is highly sought after based to the glass formulation. That being said, many lenses having thoriated glass are, coincidentally, fine performers.


Steve

(I own three thorium glass lenses, two Super-Takumar 55/1.8 and an Auto Rikenon 58/1.4.)

[Dartmoor Dave]

Are they that superior in IQ or just the novelty of being a little on the radioactive side?

That depends on what you mean by "superior in IQ". If all you want is sharpness with a DSLR then you're better off using modern lenses. But if you care about the character of a lens's rendering, which is something much more personal and much harder to define, then you might just find that thoriated (and non-thoriated) legacy lenses suit your tastes.

To try to boil some of the differences down to their essence:

Modern consumer grade lenses tend to give high contrast and bright, vibrant colours even in dull light that is actually low in contrast and flat in colour. Apparently that's what the market demands. Legacy lenses (I'm talking about Takumars in particular) tend to give a more naturalistic rendering that puts the onus on the photographer to find really good light to shoot in. Shoot in flat, dull light and you'll get flat, dull results.

Modern consumer grade lenses tend to produce results with high edge contrast, giving a superficially sharper appearance to shots taken with them. Legacy lenses tend not to have such high edge contrast, and instead give you more of what's usually called micro-contrast, resulting in photographs that might look less superficially sharp at first glance but have a more three-dimensional feel.

The best modern lenses, such as the Pentax Limited series, are much less prone to over-exaggerating colour and edge contrast than the consumer grade lenses, but of course they are also expensive. The major attraction of legacy lenses for me personally is that they give me a subtler, more naturalistic rendering than modern consumer grade lenses at a very low price.

[pathdoc]

Depending on which way your politics swing and how much ionising radiation terrifies and enrages you (or not), there is also a certain cachet in having a radioactive lens.

[photoptimist]

Thorium oxide helped to improve the refractive quality of the glass. Yes, compared to similarly priced lenses at that time, they had superior IQ.

Exactly!

Thorium dioxide has a 30-50% higher refractive index than typical glasses which translates into some combination of less-curved (thinner) elements or greater bending of light to produce more compact lenses of a given focal length and aperture.

[timw4mail]

Kodak, Yashica, Mamiya, (and of course, Asahi), among others used thorium glass. From my limited knowledge, I think Asahi was the only one to have multi-coated thorium glass lenses..

Also observe that once affordable non-radioactive dopants with similar characteristics were developed, manufacturers were just as happy to use those, even in existing designs that had previously used thorium. The non-radioactive elements of the Pentax-K 50mm f/1.4 are literally drop-in replaceable with those of the radioactive SMC Tak of the same specs with zero change in performance, aside from the effects of Thorium browning, which weren't a consideration for lenses that were never conceived of as potentially being used for 40+ years.

I'm sure there were health and safety considerations (for the lens makers) that hastened the transition to non-Thorium glass.

That said, the amount of radiation is pretty much harmless for general usage.

One of these days I want to get a geiger counter to see how much radiation the lenses actually give off, and see if I have other radioactive glass.

[glasbak]

The non-radioactive elements of the Pentax-K 50mm f/1.4 are literally drop-in replaceable with those of the radioactive SMC Tak of the same specs with zero change in performance, aside from the effects of Thorium browning,

I have two PENTAx-K 1:1.4/50 lenses, both suffer from browning and are radioactive (verified with a radiation meter), just as their smc takumar predecessors.
So it is not strange they perform similar.

[Bob 256]

Since the radioactive element (Thorium) is vitrified in the glass, the spreading of any significant radioactive particles from these lenses is a non-issue and use as a camera lens poses few (if any) radiation exposure consequences. I believe there were some issues with Thorium being used in eyepieces where their close proximity to the eye could have some health issues - hence the bad reputation of "radioactive" lenses. Likewise, as said, handling of the actual Thorium material in the lens manufacturing process itself had some potential consequences that most likely hastened moving away from its use when substitutes became available, and the lenses themselves simply became a bit novel in that they activate a radiation detector.

[SteveinSLC]

Throium? Are those the lenses that are so bad you want to throwium across the room?

[stevebrot]

Here's a very in-depth analysis done in a university lab, ostensibly with much better equipment and controls than you could hope to get in a home setting :

Thanks for this resource!


Steve

[stevebrot]

I have two PENTAx-K 1:1.4/50 lenses, both suffer from browning and are radioactive (verified with a radiation meter), just as their smc takumar predecessors.
So it is not strange they perform similar.

Wow! I have never seen any K-mount lens on the standard lists. The conventional word is that thoriated glass was illegal by the mid-1970s.


Steve

(...FWIW, I have a lens that is not on the standard lists, but which I suspect is radioactive...)

[timw4mail]

Wow! I have never seen any K-mount lens on the standard lists. The conventional word is that thoriated glass was illegal by the mid-1970s.


Steve

(...FWIW, I have a lens that is not on the standard lists, but which I suspect is radioactive...)

Now we just need Geiger counters to check..

[stevebrot]

Now we just need Geiger counters to check..

Every home should have one.


Steve

[victormeldrew]

Every home should have one.


Steve

They are fairly easy to make. Just google 'DIY geiger counter' and you'll find many guides and several ready-to-build kits.