Sankyo Kohki Komura

Stumbled over these while looking thru some M42 auctions. Cant believe I have never heard of them.

Would anyone know offhand if any of these were radioactive? Specifically the 105's and 135's, either in 2.8 or 3.5 versions?

Some of them seem to have the yellowed look, but that may just be some basic amber coating.

iTrax wrote:

lot of old lenses , like Pentax Takumar's , will turn yellow with age , I have many of them,

they will not harm you.

You can remove the tint with UV light.

https://www.youtube.com/watch?v=xjGjgqZjzPM

Thanks. I am familiar with radiation in old lenses, from thorium and lanthanum. I'm not worried about any radiation harming me. Well, other than accumulated doses over time. But radiation has the possibility of harming electronics, up to and including dead pixels in the sensor. Not a given, but it can happen. Which is why I asked if these particular lenses might have thorium, because some appear yellow.

If I remember correctly some Takumars emit far more from the front of the lens. But many old lenses emit heavily to the rear.

ProfHankD wrote:

Goethe wrote:

iTrax wrote:

lot of old lenses , like Pentax Takumar's , will turn yellow with age , I have many of them,

they will not harm you.

You can remove the tint with UV light.

https://www.youtube.com/watch?v=xjGjgqZjzPM

Thanks. I am familiar with radiation in old lenses, from thorium and lanthanum. I'm not worried about any radiation harming me. Well, other than accumulated doses over time. But radiation has the possibility of harming electronics, up to and including dead pixels in the sensor. Not a given, but it can happen. Which is why I asked if these particular lenses might have thorium, because some appear yellow.

If I remember correctly some Takumars emit far more from the front of the lens. But many old lenses emit heavily to the rear.

They certainly **might** be -- but the glass additives that happened to be mildly radioactive also tended to be not too cheap, so 2nd-teir brands didn't use them much.

Short of testing them with a counter, yellowing that clears with UV exposure would be a good hint that they're radioactive.

BTW, I don't leave known radioactive lenses on cameras for storage, but I think the probability of causing structural damage to the sensor (as opposed to a "soft error" within an exposure) is near zero.

Thanks for this Prof. There is a lot of conflicting information on the web as to what we can actually expect from radioactive lenses. I understand that there are generally no immediate health concerns, but I dont agree that everything is fine and they cant hurt anyone (which I know is not what you said here). As for electronics, I have found arguments on both sides as to why sensors may or may not be affected. It all comes down to a personal choice and while I will never berate someone for their use of radioactive lenses I myself have chosen not to use them anymore. Even though I have a radioactive Mamiya Sekor on a display camera in my living room.

Heritage Cameras wrote:

Goethe wrote:

Stumbled over these while looking thru some M42 auctions.
Cant believe I have never heard of them.

There's lots of interesting information about Komura lenses here:

http://forum.mflenses.com/the-big-sankyo-kohki-komura-thread-t80068.html

Great thread, thanks for sharing that.

Heritage Cameras wrote:

Goethe wrote:

Stumbled over these while looking thru some M42 auctions.
Cant believe I have never heard of them.

There's lots of interesting information about Komura lenses here:

http://forum.mflenses.com/the-big-sankyo-kohki-komura-thread-t80068.html

Also quite a lot on this forum

Somewhere on this forum I posted the results of my calculation of the “Komuraflex” compared to the Visoflex - they are not the same extension. Be aware that some of the lenses need the extension to focus properly - not always mentioned by vendors who might not be aware of this. 200/3.5, 300/5.6, 400/6.3, 500/7.0, 800/8.0 in LTM are examples but the list is probably not conclusive.

[Edit] - here ye’are my 2016 Visoflex adapting guide - might save some serious head scratching - from my sage words at the time it seems that the web information on Visoflex was thoroughly confusing and this was further confused because the “Komuraflex” registration distance was different. I think that this would be a good starting point.

https://www.dpreview.com/forums/post/58375064

Those interested might need to read the whole thread, especially this post:

https://www.dpreview.com/forums/post/60214837

Komura Reflex Housing part #30020 - like hens teeth. The standard tube replacement for the Visoflex housing will not work on its own.

I also have quite a lot of Komura lenses and have not noticed yellowing.

Komura also made lenses for Bronica, they were quite capable lense makers.

Prices for Komura vary greatly - I think that this merely reflects the size of the product run. Some quite cheap commonly available Komuras are quite good lenses. Eg: 135/2.8

There seem to be a huge number of Komura lens types and they were made in many lens mounts and in some exotic specifications in low numbers. They had various methods of dealing with the multiple mounts including their own Uni-adapter. I have one lens that has a Telemore Adapter built in.

The faster lenses are often promoted as “Ernostars” I am not sure if they are actually Ernostar within the meaning of the type, but then I am not that good at reading lens diagrams.

My experience is that the grease used turns into a black sticky gunk in time. The ones that relate to the Sonnar build type will screw apart in the middle and updating the helicoid grease is not a huge business.

My very first Komura lens purchase came effectively locked solid focus due to that black grease. Others where the focus was silky obviously had been re-greased before I purchased it.

Tom Caldwell wrote:

Heritage Cameras wrote:

Goethe wrote:

Stumbled over these while looking thru some M42 auctions.
Cant believe I have never heard of them.

There's lots of interesting information about Komura lenses here:

http://forum.mflenses.com/the-big-sankyo-kohki-komura-thread-t80068.html

Also quite a lot on this forum

Somewhere on this forum I posted the results of my calculation of the “Komuraflex” compared to the Visoflex - they are not the same extension. Be aware that some of the lenses need the extension to focus properly - not always mentioned by vendors who might not be aware of this. 200/3.5, 300/5.6, 400/6.3, 500/7.0, 800/8.0 in LTM are examples but the list is probably not conclusive.

[Edit] - here ye’are my 2016 Visoflex adapting guide - might save some serious head scratching - from my sage words at the time it seems that the web information on Visoflex was thoroughly confusing and this was further confused because the “Komuraflex” registration distance was different. I think that this would be a good starting point.

https://www.dpreview.com/forums/post/58375064

Those interested might need to read the whole thread, especially this post:

https://www.dpreview.com/forums/post/60214837

Komura Reflex Housing part #30020 - like hens teeth. The standard tube replacement for the Visoflex housing will not work on its own.

I also have quite a lot of Komura lenses and have not noticed yellowing.

Komura also made lenses for Bronica, they were quite capable lense makers.

Prices for Komura vary greatly - I think that this merely reflects the size of the product run. Some quite cheap commonly available Komuras are quite good lenses. Eg: 135/2.8

There seem to be a huge number of Komura lens types and they were made in many lens mounts and in some exotic specifications in low numbers. They had various methods of dealing with the multiple mounts including their own Uni-adapter. I have one lens that has a Telemore Adapter built in.

The faster lenses are often promoted as “Ernostars” I am not sure if they are actually Ernostar within the meaning of the type, but then I am not that good at reading lens diagrams.

My experience is that the grease used turns into a black sticky gunk in time. The ones that relate to the Sonnar build type will screw apart in the middle and updating the helicoid grease is not a huge business.

My very first Komura lens purchase came effectively locked solid focus due to that black grease. Others where the focus was silky obviously had been re-greased before I purchased it.

Thank you Tom. LOTS of good info there.