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Is the SMC Pentax K 55/1.8 radioactive as the Tak version?
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PostPosted: Wed Oct 13, 2021 10:21 am    Post subject: Is the SMC Pentax K 55/1.8 radioactive as the Tak version? Reply with quote

Hello,

Is the K series SMC Pentax 55mm F1.8 radioactive as the Takumar 55m F1.8 that it is based on? The internet lists of radioactive lenses do not include the K version and this is the reason I ask. Perhaps they changed the glass formula for the K series?

I understand that the radioactivity of the Takumar is not something really dangerous but I have an eye condition that should exclude any presence or use of radioactive objects as much a possible so this is an important question in my case.

Thanks in advance!


PostPosted: Wed Oct 13, 2021 10:50 am    Post subject: Reply with quote

According to this it isn't http://fockert.xs4all.nl/~pentax/radioactive_lenses/radioactive.html

My copy doesn't seem to display any yellowing but the same can be said for my SMC (not S-M-C) Takumar 55 1.8 which apparently is radioactive, or maybe it isn't and Pentax changed it at some point. I'd say the SMC Pentax 55mm 1.8 probably isn't radioactive. Pentax made the K-mount lenses slightly larger than the screw mount ones. 52mm filter size instead of 49mm (Before Pentax-m) so they probably updated the lens calculation as well without thoriated glass (except for the SMC 50mm 1.4, which is radioactive).


PostPosted: Wed Oct 13, 2021 11:28 am    Post subject: Reply with quote

D1N0 wrote:
According to this it isn't http://fockert.xs4all.nl/~pentax/radioactive_lenses/radioactive.html

My copy doesn't seem to display any yellowing but the same can be said for my SMC (not S-M-C) Takumar 55 1.8 which apparently is radioactive, or maybe it isn't and Pentax changed it at some point. I'd say the SMC Pentax 55mm 1.8 probably isn't radioactive. Pentax made the K-mount lenses slightly larger than the screw mount ones. 52mm filter size instead of 49mm (Before Pentax-m) so they probably updated the lens calculation as well without thoriated glass (except for the SMC 50mm 1.4, which is radioactive).


Thank you! It seems like a lens that really matches my preferences for rich colors and contrast with decent sharpness wide open - now I can safely and gladly buy one!


PostPosted: Thu Oct 14, 2021 6:53 pm    Post subject: Reply with quote

Dusty-Lens wrote:
Thank you! It seems like a lens that really matches my preferences for rich colors and contrast with decent sharpness wide open - now I can safely and gladly buy one!


Just FYI, the earlier Auto Takumar 55 1.8 and the earliest version of the Super Takumar 55 1.8 are not radioactive. Those two lenses look nearly identical.

You can tell the early Super Takumars by the aperture ring, which has tiny, evenly-spaced teeth. The much-more-common radioactive version has an aperture ring with larger scallops.

I mention this just in case you want to try a Super Takumar 55 1.8 that isn't radioactive.


PostPosted: Thu Oct 14, 2021 7:14 pm    Post subject: Reply with quote

KEO wrote:
Dusty-Lens wrote:
Thank you! It seems like a lens that really matches my preferences for rich colors and contrast with decent sharpness wide open - now I can safely and gladly buy one!


Just FYI, the earlier Auto Takumar 55 1.8 and the earliest version of the Super Takumar 55 1.8 are not radioactive. Those two lenses look nearly identical.

You can tell the early Super Takumars by the aperture ring, which has tiny, evenly-spaced teeth. The much-more-common radioactive version has an aperture ring with larger scallops.

I mention this just in case you want to try a Super Takumar 55 1.8 that isn't radioactive.


Thank you!

I just asked a very kind and cooperative ebay seller to measure a late SMC Takumar 55mm f/2.0 version and he said that the meter showed no difference from the background which is quite interesting.

Is the newer K series SMC Pentax 55/1.8 possibly anyhow better or worse optically than the SMC Takumar 55/1.8? I am asking as they can be bought for the same price basically and perhaps I should consider the better version.


PostPosted: Thu Oct 14, 2021 11:30 pm    Post subject: Reply with quote

If there are differences they are probably down to build quality. My SMC Pentax 55mm is built like a dream, whereas my otherwise good looking SMC Takumar 55mm 1.8 has some stiffness in the (rubberised) focussing ring. The SMC K series probably have the best build quality of all pentax lenses.


PostPosted: Fri Oct 15, 2021 6:31 am    Post subject: Reply with quote

D1N0 wrote:
If there are differences they are probably down to build quality. My SMC Pentax 55mm is built like a dream, whereas my otherwise good looking SMC Takumar 55mm 1.8 has some stiffness in the (rubberised) focussing ring. The SMC K series probably have the best build quality of all pentax lenses.


Thank you for the clarification! Both the SMC Taks and the K series look like they are some of the best built lenses indeed.


Last edited by Dusty-Lens on Sat Oct 16, 2021 10:10 am; edited 1 time in total


PostPosted: Sat Oct 16, 2021 10:02 am    Post subject: Reply with quote

D1N0 wrote:
If there are differences they are probably down to build quality. My SMC Pentax 55mm is built like a dream, whereas my otherwise good looking SMC Takumar 55mm 1.8 has some stiffness in the (rubberised) focussing ring. The SMC K series probably have the best build quality of all pentax lenses.


That’s not my experience. I think the metal ring Takumars are the best. Never had one with a problem yet. With the K series I had, half of them had something, like stiffness. Still very well built lenses though.


PostPosted: Sat Oct 16, 2021 10:25 am    Post subject: Reply with quote

caspert79 wrote:
D1N0 wrote:
If there are differences they are probably down to build quality. My SMC Pentax 55mm is built like a dream, whereas my otherwise good looking SMC Takumar 55mm 1.8 has some stiffness in the (rubberised) focussing ring. The SMC K series probably have the best build quality of all pentax lenses.


That’s not my experience. I think the metal ring Takumars are the best. Never had one with a problem yet. With the K series I had, half of them had something, like stiffness. Still very well built lenses though.


I have experienced stiffness or unevenness with several Takumars especially the more mass produced ones. None of My K series primes are stiff. Zooms are another story, zooming can get pretty uneven.