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06-25-2013, 02:29 PM   #16
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QuoteOriginally posted by stevebrot Quote
Apples and bananas
Steve
Indeed but still.
Scaring someone when tehre are more damaging things around us is just silly, it's almost a kind of fobia...

06-25-2013, 03:58 PM   #17
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Nuclear engineer refuses granite countertops

I have a friend with Ph.D. in nuclear enoineering--he worked for a nuclear utility company for over 3 decades (part of the time in my analysis group) and when he purchased a home he worried about the radioactiviity due to the granite counter tops.

Give the OP a break--he asked a simple question. It's not your guys place to tell him to change his religion.
06-25-2013, 04:06 PM   #18
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One more thing--in the nuclear industry the work involving radioactivity is done under the term ALARA--which stands for As Low As Reasonably Possible.
06-25-2013, 05:10 PM   #19
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QuoteOriginally posted by ArticFox Quote
Don't quote me, but I believe that the Pentax LX can AE for many minutes with changing light better than anyone, except for perhaps the OM2/4.
Olympus claimed an EV range of -6.5 to 19 for the OM 4 meter. The Pentax LX is said to be -6.5 to 20 EV. The OM 4 had a maximum exposure of 240s in auto mode, the LX 125s. The OM 4 had a spot meter, but the LX had interchangeable viewfinders as well as focusing screens.

Pentax manufactured the LX for 21 years and never updated it, something I'll never understand. It's a great camera, but it would have been nice to have Tv mode...

06-25-2013, 05:51 PM   #20
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Your concern is noted

QuoteOriginally posted by ArticFox Quote
Boriscleto, Stevebrot, scratchpaddy, and TomB_tx, - thank you for your sincere and interesting responses. Although it was not my intent, radioactivity in a lens was a good topic to test the personality of a forum. Some forums such as Photo.net, an Miranda are nice and few in between, so it will be interesting to see how Pentax Forums holds out over time.

The Helios 44 is mentioned in one of the best forum strings I have ever encountered on Miranda's "most magical lenses". I spent more than a month reviewing that string.

After you mention it, radioactive lenses do seem prominent in fast glass.

I do not have a Pentax yet, but I have my eyes on the Spotmatic and K family. Some time ago I tested the MX, but its size and balance was not there for me, but I should have tested a motor-drive with it. My guru repair guy for Leica (I don't intend to own a Leica) claims that the MX is internally the best built Pentax, without any other factors in consideration. I like mechanical cameras in concept, but, with my classic Nikons, I value the extended and less discrete shutter speed range that AE offers. Don't quote me, but I believe that the Pentax LX can AE for many minutes with changing light better than anyone, except for perhaps the OM2/4. I am also a big fan of a large, bright, and clear viewfinder, focus snap, and nice manual focus rings on the lens. I use a 10x compact Ziess binocular daily, so these things I like with cameras are probably associated with binocular use.
I don't actually own any Pentax or Leica lenses . . .
06-25-2013, 06:39 PM   #21
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QuoteOriginally posted by stevebrot Quote
Except that the OP uses a Spotamatic (M42). In that mount, radioactive elements are more common than in the later K-mount glass. In the Pentax line, this would include both the S-M-C and SMC Takumars. A generalization may be made that thoriated glass is generally more common in faster lenses at the normal and wider focal lengths, so I would think that most 28mm and 35mm lenses at f/2.8 are probably pretty "cold". Ditto for 135mm at f/2.8.


Steve

Quite often: the purpose of the thoriated glass is actually generally to reduce the size of fast, wider lenses, so that seems to be where they're found. My only real concern with mine, (actually it's the FD 35/2 for my old Canons) is that that the radiation may be a problem if left close to film I'm going to push. (Though something else may be the source of that problem, I need to do a bit more experimenting to be sure, though. (it might be that someone X-rayed a batch of film I ordered in the mail or something)
06-26-2013, 05:48 AM   #22
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Welcome on board ArticFox -- I think of the KX and K2 as K mount Spotmatics. Mechanical cameras are wonderful; the early AE ones (ES II) have limited manual exposure ability. After the K series, Pentax went small; some people like that and some don't. The pre Spotmatic Pentax cameras are the most Leica-like, in that they are very smooth and ballerina-like. No metering though.
06-26-2013, 06:04 AM   #23
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Thorium Isotopes are mostly alpha particle* emitters, the only beta particle emitter Isotopes have rather short half lives. Unless you actively decide to grind up the glass and eat it, or inhale the dust it these lenses pose no serious threat. Your total exposure to background radiation over the year is more significant than any exposure you will get from using radioactive lenses. The most dangerous aspect of radioactive materials is when they become aerosolized as dust, in this situation virtually any radioactive material can be hazardous. But the glass elements in a lens are solid, there is no way short of pulverizing the glass to dust that would allow the thorium used in them to become a danger to anyone.

* Alpha particles can be stopped by a few molecules of air - in fact it is entirely possible to juggle balls of solid plutonium 239 without injury ( unless you drop them on your foot, but that would be harmful even if they were made of steel). The same cannot be said for strontium 90. When it comes to radioactive elements: Generally the shorter the half-life, the nastier the material is. For instance: Astatine 210 has a half-life less than 8 hours - and it is so intensely radioactive, and for this reason it has not been as comprehensively analyzed like other radioactive materials like Uranium.


Last edited by Digitalis; 06-26-2013 at 06:33 AM.
06-26-2013, 06:18 AM   #24
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QuoteOriginally posted by ArticFox Quote
I still wish to explore the Spotmatics. Do I have options with quality non radioactive M42 Pentax or other M42 brands?
As has been mentioned, the 55/1.8 or f/2 is not radioactive, and is a very fine lens. I like the Yashica lenses - DX, DM etc; these are not radioactive. Ditto for Fujinons.

Now that I think of it, the KX I find very similar to the FE Nikon, in the viewfinder at least. Similar metering readouts.
06-26-2013, 08:59 AM   #25
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QuoteOriginally posted by boriscleto Quote
Olympus claimed an EV range of -6.5 to 19 for the OM 4 meter. The Pentax LX is said to be -6.5 to 20 EV. The OM 4 had a maximum exposure of 240s in auto mode, the LX 125s. The OM 4 had a spot meter, but the LX had interchangeable viewfinders as well as focusing screens.

Pentax manufactured the LX for 21 years and never updated it, something I'll never understand. It's a great camera, but it would have been nice to have Tv mode...
Well, in those years, a lot of serious shooters were fairly skeptical of automation anyway, and adding Tv mode would have been messing with something already considered about the best for a certain style of shooter.

(And, right, Digitalis: the real reason they stopped making 'radioactive lenses' is because they were hazardous to manufacture for the workers. )
06-26-2013, 09:55 AM   #26
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QuoteOriginally posted by Nesster Quote
the 55/1.8 or f/2 is not radioactive
Except for in the small study I linked to. Though in all fairness, the gamma count for that lens was much less than the ST 50/1.4.

Yes, gamma. Thorium decays by alpha emission with accompanying gamma radiation. What that means is that the atom spits out an alpha particle (essentially the same as a helium nucleus) and briefly "glows" with gamma waves. (Gamma is ionizing electromagnetic radiation with a wavelength somewhat shorter than x-ray.) Alpha particles are not particularly hazardous, while gamma may be.

The link I supplied above is interesting to me because the person who did it used a Geiger counter for initial screen (would count both alpha and gamma) followed a different setup using a gamma-specific scintillation detector.


Steve
06-26-2013, 01:21 PM   #27
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The Best Pentax Repair Guys

I decided to begin with the K series and the PK mount, and bought a K2 for $50. Of course, a CLA will reveal its condition.

Does anyone have a forum reference to the best classic Pentax CLA/repair guys?

I have an idea about favorite lens focal lengths, but will have to study first generation PK mount lens options.
06-26-2013, 01:45 PM   #28
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QuoteOriginally posted by ArticFox Quote
I decided to begin with the K series and the PK mount, and bought a K2 for $50. Of course, a CLA will reveal its condition.

Does anyone have a forum reference to the best classic Pentax CLA/repair guys?

I have an idea about favorite lens focal lengths, but will have to study first generation PK mount lens options.
You will likely get more traction if you start a new thread.

That being said, the conventional wisdom here is Eric Hendrickson in Tennessee

Pentax Repair


Steve
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