Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-11-2017, 09:16 PM   #1
Junior Member
cdd29's Avatar

Join Date: Sep 2016
Location: Southern Indiana
Photos: Gallery
Posts: 33
throium glass lenses

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?

10-11-2017, 10:13 PM   #2
Site Supporter
Alex645's Avatar

Join Date: May 2015
Location: Kaneohe, HI
Photos: Albums
Posts: 1,338
Thorium oxide helped to improve the refractive quality of the glass. Yes, compared to similarly priced lenses at that time, they had superior IQ.
10-12-2017, 12:00 AM   #3
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,438
QuoteOriginally posted by cdd29 Quote
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.)
6 Days Ago - 1 Like   #4
Site Supporter
Dartmoor Dave's Avatar

Join Date: Aug 2012
Location: Dartmoor, UK
Photos: Albums
Posts: 972
QuoteOriginally posted by cdd29 Quote
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.

6 Days Ago   #5
Loyal Site Supporter




Join Date: Mar 2015
Photos: Gallery | Albums
Posts: 5,805
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.
6 Days Ago   #6
Pentaxian
dcshooter's Avatar

Join Date: Jan 2011
Location: Washington DC
Photos: Gallery | Albums
Posts: 4,603
QuoteOriginally posted by stevebrot Quote
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.)
This exactly. Recall that the Thorium doping was used to magnify the differences in reffraction between paired elements, allowing for stronger corrections, which in turn allowed for (but doesn't necessarily have to imply) better corrected lens designs. So a design might have thoriated elements because it was an innovative or high performing design for its time, but this doesn't imply that the reverse is true. Thorium was just a tool in the lens designers' toolbox, and it was up to the lens designers to use it, effectively or not.

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.

There's nothing magic about the thorium. It was just the most economical way to hit the specs produced by designers at the time.

Last edited by dcshooter; 6 Days Ago at 06:22 AM.
6 Days Ago   #7
Pentaxian
photoptimist's Avatar

Join Date: Jul 2016
Photos: Albums
Posts: 1,381
QuoteOriginally posted by Alex645 Quote
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.
6 Days Ago   #8
Site Supporter
timw4mail's Avatar

Join Date: Apr 2017
Location: Lansing, MI
Photos: Gallery | Albums
Posts: 612
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..

QuoteOriginally posted by dcshooter Quote
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.

6 Days Ago   #9
Pentaxian
dcshooter's Avatar

Join Date: Jan 2011
Location: Washington DC
Photos: Gallery | Albums
Posts: 4,603
QuoteOriginally posted by timw4mail Quote


I'm sure there were health and safety considerations (for the lens makers) that hastened the transition to non-Thorium glass.
Sure, of course. My statement was only meant to comment on the similarity of performance characteristics of thorium and the dopants that replaced it. Health and safety are, after all, part of the economic equation in choosing materials.


QuoteOriginally posted by timw4mail Quote

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.
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 :

http://www.diva-portal.org/smash/get/diva2:652338/FULLTEXT01.pdf

The upshot is that emission is not very high, and potential absorption is even lower (i.e. 0.2% of maximum annual exposure to the eye and 0.17% total body for an 8 hour a day user of the hottest lens they tested, a Zeiss Tessar).
6 Days Ago   #10
Veteran Member
glasbak's Avatar

Join Date: Apr 2009
Location: Netherlands
Posts: 346
QuoteOriginally posted by dcshooter Quote
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.
6 Days Ago   #11
Senior Member




Join Date: Jun 2008
Location: Idaho
Photos: Gallery
Posts: 189
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.
6 Days Ago   #12
Site Supporter




Join Date: Mar 2017
Posts: 23
Throium? Are those the lenses that are so bad you want to throwium across the room?
6 Days Ago   #13
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,438
QuoteOriginally posted by dcshooter Quote
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
6 Days Ago   #14
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,438
QuoteOriginally posted by glasbak Quote
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...)
6 Days Ago   #15
Site Supporter
timw4mail's Avatar

Join Date: Apr 2017
Location: Lansing, MI
Photos: Gallery | Albums
Posts: 612
QuoteOriginally posted by stevebrot Quote
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..
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
glass, k-mount, lenses, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
PENTAX new glass-old glass - lens tubes designed like old glass? corporate identity? camyum Pentax Full Frame 3 09-24-2017 02:52 PM
New glass - old glass. Which lenses should Pentax revisit? HopelessTogger Pentax Full Frame 204 09-07-2017 05:12 AM
Glass is glass right?? Raptorman Pentax SLR Lens Discussion 15 11-11-2009 01:56 PM
Autumn colors - old glass is a good glass andrei46 Post Your Photos! 5 10-26-2007 09:35 AM



All times are GMT -7. The time now is 12:56 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top