Older lenses with THORIUM element

I have been reading this forum for about the last month since I learned of

it's existence. What seens very fascinating is the lenses that were made with

the Thorium elements. Were the 35mm concave element SSC lenses the only one

that had the Thorium element? Are there other lenses in the line-up that also

had this element? I shoot Black and White almost exclusively and would very

much like to aquire some of these fine lenses. Thanks,.....Ray

The only lens I have ever heard of in the Canon FD line up with the Thorium element is the first four versions of the 35mm f2.0.

 

The first chrome nose versions are always Thorium and those later marked S.S.C. with the concave front element are also Thorium.

 

There is an excellent write on these on the Canon FD FAQ site here:

 

http://www.farah.cl/CanonFD/CanonFD_faql.html#35mm

 

I have a very nicely ambered Chrome nose first version as well as a later 35mm f2.0 nFD (that of course is not ambered or containing Thorium.

 

But if your looking for other sleepers in the FD line up the 135mm f2.5 Chrome nose or S.C. is a great portrait lens to have is the hard to find 135mm f3.5 Chrome Nose (this lens has a very simple Tessar type formula)

 

For a great sharp lens look for the 100mm f2.8 Chrome Nose or S.S.C.

 

And for a real fast lens don't over look the 55mm f1.2 Chrome nose if you have a large wallet heavy with money look for the 55mm f1.2 Asperical you can not do better if your looking for a std. lens.

(i) Ray-- if you're buying a 35/2.0 SSC and you don't have it in your hand (like if you're buying it online), the first version (concave front glass) only goes to f/16. The later versions (convex) went to f/22. This is a useful distinguishing point.

 

(ii) Mark, different topic: about the early 135/3.5 FD lens, what's the evidence that it's a tessar design? I couldn't find an optical block diagram for this anywhere. FWIW, the 135/3.5 for the rangefinder Canons was four elements in three groups, but it was not a tessar. It had a Sonnar-like thick cemented two-element group in the center, although the rear element was single.

Dave I think you could be right. I wasn't sure as I was typing it being a tessar formula which is 4 elements in three groups.

 

The early 135mm f3.5 CN has the same 4 elements in 3 groups. It is the same formula as the FL lens. I have a block diagram in my 1969 Canon lens book. But now looking at a Tessar formula the arrangement of th elements is different. I should have looked at the Tessar formula before assuming the formula would be the same just because they are both 4 in 3.

 

I stand corrected.

I have both the 35mm 2/f FD SSC concave front element lens and the 135/3.5 chrome front. The 35/2 is quite yellow by now and I will need to look up the threads on getting the color to fade with UV or sunlight. When I knew I wanted to shoot some color slide film I bought a 35/2 New FD lens and that's the one I have been using more. It's also a very good lens but has a clear color. I also like the 135/3.5 chrome front lens. It's heavy as lead and has a nice feel to it.

In addition to the Thorium aspect, are they also unique among FD lenses for the concave front element? To me a concave front glass on a wide lens has always seemed bizarre and wonderful, especially given the usual trend for more and more convex front surfaces on wides. Does anybody have any insight as to why the optical design would call for the concave first element?

 

As a slide note, I have always wanted one of these lenses. And I think that if I were a collecter I would just HAVE to have one! Radioactive Thorium glass; concave front element; excellent reputation for image quality (especially in terms of B&W with a "built in" yellow filter). How cool can you get!

 

Jeff

The only other lens with a concave front element that I am aware of is the Leica M 35mm

1.4 Summilux ASPH lens introduced in 1991. Only an optical lens engineer could give an

accurate answer why. Just keep in mind that the front element is only a part of the optical

formula.

 

For the money, the CN a steal & one of the best B&W lenses IMHO you could own. Usually

sells for around $150. Another sleeper lens to consider is the Pentax 50mm 1.4 SMCT

screwmount used with the Canon P adapter. Best $50 I ever spent.

This site : http://www.orau.org/ptp/collection/consumer%20products/cameralens.htm claims that the early 58/1.2 was a thorium lens. I can't confirm, having not had one. Steve

Steve that site has info that does not jive with the real world. Kodak made a bunch of huge lenses for use in airborne cameras during WWII They even had a problem with storing a bunch of them in one place at the Eastman House museum (I guess the ares got a little "Hot") The writer does not list the 35mm f2.0 we are talking about. The two versions of the 58mm f1.2FL the 1964 and 1966 both appear to have very normal looking Double Gauss formulas. So I don't see any indication of a Thorium element formula.

1) Thorium is radioactive (http://theodoregray.com/PeriodicTable/Elements/090/)

Don't carry a thorium lens in your sporran for a long time! It can also fog film in the camera.

 

2) lens elements with it tend to turn yellow brown

 

 

3) of no real relevance, but the Pony 135 had a thoriated lens.

The tiny amount of radiation coming off a 35mm f2.0 would take a very very long time to fog film. After all a dozen passes through an airport X Ray machine won't have an visable effect.

 

The lens elements do not turn brow or amber or yellow it is the cement layer that changes

 

As to sterilization well for some of us I think that might be a good idea!

I don't think that your film would be at too much risk even with the lens sitting on top of it.

 

Background cosmic radiation amounts to about 240 mrem annually.

 

According to the above length, the average dose to a human using a camera with the thoriated lens element 10 cm away is .01 mrem/hr. This means that with your film sitting about 10 cm away from the lens, over the course of a year, it will receive about 4 months worth of background radiation from the lens.

 

There's a good chance you won't be leaving your film in your bag for a year at a time, or that you'll have the lens and film a lot further 10 cm away from each other, so radiation from the lens really isn't significant in that context. Background cosmic radiation is a lot more significant.

Of course, 90% of what is on the internet is crap. That used to bother me until I discovered an old Abe Maslow quote on my refrigerator that 90% of EVERYTHING is crap! Certainly some such claim can even be made for this thread.

 

Coming from that statement, if you check out the physics sites on the internet about this, some of them (in the 90% or the 10%?) don't seem to think that the radiation level of some of these lenses was all that trivial, and it was from them that I got the idea that film should not be left for long periods in a camera with one of these lenses. Like those ladies licking their radium paint brushes as they were painting watch dials, standards do change. Ditto, Fiesta ware pottery. They still tell the dying workers from the local weapons-grade plutonium plant that their cancers can't have had anything to do with work related exposure since that was all within the health guidelines of the times.

 

Yes, whatever about the color change, I can't speak to what exactly changes color, but it is certainly not unheard of for glass to change color under various kinds of radiation. The point was that the lens as whole does become yellow or brown. Merely noted since it makes them less than desirable as working lenses. There are various fixes proposed such as exposure to the sun for long periods, but by far the most effective repair is that of Brian Ayling for affected Takumars presented at what should be one of the most popular sites on the web: http://www.hermes.net.au/bayling/repair.html .

 

Finally, if sterilization is your wish, castration or other neutering is probably more effective in pulling you out of the gene pool than carrying a thoriated lens.

I can confirm that the old FL 58mm F/1.2 is a thorium lens, indeed. I have one, and it has a really good bokeh, great fast aperture, and a wonderful amber cast. B&W comes out fine though, and it's a very good deal if you can find one.

The 35/2 is a lovely lens. I only stopped using it lately because I shoot mostly 6x9. But you can scan and stitch 35mm frames and get MF quality from that lens. Also, I have a color preset calibration for scanning frames shot with the 35/2 that renders them indistinguishable from the 50/1.4 palette. A stitching example: http://www.photo.net/photo/3909563