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08-09-2019, 12:14 PM   #16
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The K version has the better mechanics(brass on aluminum in the focus heliocoid) and the radioactive yellowing/browning glass (hence the warmer cast),

08-09-2019, 01:59 PM   #17
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08-09-2019, 05:22 PM   #18
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QuoteOriginally posted by glasbak Quote
The K version has the better mechanics(brass on aluminum in the focus heliocoid) and the radioactive yellowing/browning glass (hence the warmer cast),
These are the known Pentax lenses that contain thoriated element(s), copied from Camerapedia. I’ve bolded those on this list that I own or have owned.

SMC Pentax 50mm f/1.4 (original "K line")*
SMC Takumar 20mm f/4.5
SMC Takumar 35mm f/2.0 (Asahi Optical Co.)*
Super Takumar 35mm f/2.0 (Asahi Optical Co.)
SMC Takumar 50mm f/1.4 (Asahi Optical Co.) (both knurled and rubber focus ring grip versions)*
Super Takumar 50mm f/1.4 (only the latest version with 7 elements
SMC Macro Takumar 50mm f/4.0*
Super Takumar 55mm f/1.8 (Asahi Optical Co.)
Super-Multi-Coated Takumar 55mm f/1.8 (Asahi Opt. Co.)
SMC Takumar 55mm f/1.8 (Asahi Optical Co.)*
Super Takumar 55mm f/2.0 (Asahi Optical Co.)
SMC Takumar 55mm f/2.0 (Asahi Optical Co.)*
SMC Takumar 85mm f/1.8 (Asahi Optical Co.)*
Super Takumar 6x7 105mm f2.4 (Asahi Optical

All of my thoriated lenses have been fully cleared by exposure to UV light. None of them has any yellow cast whatsoever. My impresssion of the rendering noted above applies consistently across my entire collection of K series lenses (I have all but one of them) and compares across the many M and A lenses I have of similar focal lengths, as stated above. The K50/1.4 is the only SMC Pentax (K) lens reported to contain thoriated elements.

IMO the warmer rendering of the K lenses is not related to the presence of thoriated glass in the SMC PENTAX (K) 50/1.4.

* I own The K version of these lenses.

Last edited by monochrome; 08-09-2019 at 05:50 PM.
08-09-2019, 06:11 PM   #19
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QuoteOriginally posted by monochrome Quote
These are the known Pentax lenses that contain thoriated element(s), copied from Camerapedia. I’ve bolded those on this list that I own or have owned.

SMC Pentax 50mm f/1.4 (original "K line")*
SMC Takumar 20mm f/4.5
SMC Takumar 35mm f/2.0 (Asahi Optical Co.)*
Super Takumar 35mm f/2.0 (Asahi Optical Co.)
SMC Takumar 50mm f/1.4 (Asahi Optical Co.) (both knurled and rubber focus ring grip versions)*
Super Takumar 50mm f/1.4 (only the latest version with 7 elements
SMC Macro Takumar 50mm f/4.0*
Super Takumar 55mm f/1.8 (Asahi Optical Co.)
Super-Multi-Coated Takumar 55mm f/1.8 (Asahi Opt. Co.)
SMC Takumar 55mm f/1.8 (Asahi Optical Co.)*
Super Takumar 55mm f/2.0 (Asahi Optical Co.)
SMC Takumar 55mm f/2.0 (Asahi Optical Co.)*
SMC Takumar 85mm f/1.8 (Asahi Optical Co.)*
Super Takumar 6x7 105mm f2.4 (Asahi Optical

All of my thoriated lenses have been fully cleared by exposure to UV light. None of them has any yellow cast whatsoever. My impresssion of the rendering noted above applies consistently across my entire collection of K series lenses (I have all but one of them) and compares across the many M and A lenses I have of similar focal lengths, as stated above. The K50/1.4 is the only SMC Pentax (K) lens reported to contain thoriated elements.

IMO the warmer rendering of the K lenses is not related to the presence of thoriated glass in the SMC PENTAX (K) 50/1.4.

* I own The K version of these lenses.
And this is the only source that claims the K is thoriated. The "testing" method for most of these lenses is "Hold an old dosimeter I bought on eBay up to the back of the lens".

08-09-2019, 06:14 PM   #20
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QuoteOriginally posted by boriscleto Quote
And this is the only source that claims the K is thoriated. The "testing" method for most of these lenses is "Hold an old dosimeter I bought on eBay up to the back of the lens".
Yep. But I chose not to contest that point here.
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