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Mamiya Sekor CS 135/2.8 Aperture Return Spring
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PostPosted: Fri Jun 26, 2020 12:27 pm    Post subject: Mamiya Sekor CS 135/2.8 Aperture Return Spring Reply with quote
Hi All

Does anyone have any experience with the internal workings of the Mamiya CS lenses, specifically the 135/2.8? A few years back I bought an NC1000S camera with four CS lenses at a car boot sale ... it's been sitting in a cupboard since. With the CoVID-19 lock down I've had time to tinker with the camera and lenses ... noticed that the 135/2.8 had oiled aperture blades so I decided to clean them up. This is something I've done many times before on other lenses. Once cleaned and fully operational I reassembled, all now works but not perfectly.

The main issue is the return mechanism on the aperture. The aperture is normally open, held open by a spring located horizontally within the lens body right next to the blades (it's like the spring in a biro). It is this spring that seems to provide the tension against which the whole stop down mechanism operates. The stopping down part works fine but the spring provides very little 'snap back'. The stop down mechanism itself has multiple parts, each of which adds some friction, the sum of which has to be overcome by the spring to provide enough energy to snap the aperture back open again.

All the parts are completely clean, and the blades snap open fine but return to about 75% of their open position (so at F16 the aperture only returns top about the F5.6 position for instance, and for F2.8 and F4 the blades snap back fully). The other CS lenses I have all have much more positive stop down mechanisms, but they don't look to be the same constructions as the 135.

Can anyone advise?

Thanks


PostPosted: Fri Jul 03, 2020 12:47 pm    Post subject: Reply with quote
Welcome Zuikomar


PostPosted: Sat Jul 04, 2020 9:07 am    Post subject: Re: Mamiya Sekor CS 135/2.8 Aperture Return Spring Reply with quote
Zuikomar wrote:
Hi All

Does anyone have any experience with the internal workings of the Mamiya CS lenses, specifically the 135/2.8? A few years back I bought an NC1000S camera with four CS lenses at a car boot sale ... it's been sitting in a cupboard since. With the CoVID-19 lock down I've had time to tinker with the camera and lenses ... noticed that the 135/2.8 had oiled aperture blades so I decided to clean them up. This is something I've done many times before on other lenses. Once cleaned and fully operational I reassembled, all now works but not perfectly.

The main issue is the return mechanism on the aperture. The aperture is normally open, held open by a spring located horizontally within the lens body right next to the blades (it's like the spring in a biro). It is this spring that seems to provide the tension against which the whole stop down mechanism operates. The stopping down part works fine but the spring provides very little 'snap back'. The stop down mechanism itself has multiple parts, each of which adds some friction, the sum of which has to be overcome by the spring to provide enough energy to snap the aperture back open again.

All the parts are completely clean, and the blades snap open fine but return to about 75% of their open position (so at F16 the aperture only returns top about the F5.6 position for instance, and for F2.8 and F4 the blades snap back fully). The other CS lenses I have all have much more positive stop down mechanisms, but they don't look to be the same constructions as the 135.

Can anyone advise?

Thanks


I have converted the mounts of the CS 35mm 2.8 and 135mm 2.8 lenses to EF mount (Canon, not Mamiya EF) and in that process reversed the aperture springload so it was no longer dependent on the original camera functions. This will not help you much in use on a Mamiya SLR but I think that if you use a bit of teflon spray fluid at the right spots far from the blades it may help with a weakened spring. Otherwise find a suitable spring to replace it or shorten the existing spring (which will end its useful life even faster though).

I am very fond of the CS 35mm 2.8 on an A7RII but the 135mm 2.8 shows a lot of CA and purple fringing. Could be my sample. I bought it after the 35mm as it was described as very good and scored high on the list of lightest 135mm 2.8's.


PostPosted: Sun Jul 05, 2020 9:10 pm    Post subject: Reply with quote
Interesting. I have a Sony A7ii, which I use with many lenses, but not the Mamiya CS lenses. I also have the 35/2.8, 50/1.7 and 50/3.5 Macro CS lenses. Hadn't thought about converting them ... do you use an adapter or have you actually reworked the mount in some way?


PostPosted: Mon Jul 06, 2020 12:21 am    Post subject: Re: Mamiya Sekor CS 135/2.8 Aperture Return Spring Reply with quote
Zuikomar wrote:
Hi All

Does anyone have any experience with the internal workings of the Mamiya CS lenses, specifically the 135/2.8? A few years back I bought an NC1000S camera with four CS lenses at a car boot sale ... it's been sitting in a cupboard since. With the CoVID-19 lock down I've had time to tinker with the camera and lenses ... noticed that the 135/2.8 had oiled aperture blades so I decided to clean them up. This is something I've done many times before on other lenses. Once cleaned and fully operational I reassembled, all now works but not perfectly.

The main issue is the return mechanism on the aperture. The aperture is normally open, held open by a spring located horizontally within the lens body right next to the blades (it's like the spring in a biro). It is this spring that seems to provide the tension against which the whole stop down mechanism operates. The stopping down part works fine but the spring provides very little 'snap back'. The stop down mechanism itself has multiple parts, each of which adds some friction, the sum of which has to be overcome by the spring to provide enough energy to snap the aperture back open again.

All the parts are completely clean, and the blades snap open fine but return to about 75% of their open position (so at F16 the aperture only returns top about the F5.6 position for instance, and for F2.8 and F4 the blades snap back fully). The other CS lenses I have all have much more positive stop down mechanisms, but they don't look to be the same constructions as the 135.

Can anyone advise?

Thanks

This is what I am afraid of for the topcor lenses that I mentioned in another post. I guess you can find a way to shorten the spring to make it stronger.


PostPosted: Mon Jul 06, 2020 7:32 am    Post subject: Reply with quote
Zuikomar wrote:
Interesting. I have a Sony A7ii, which I use with many lenses, but not the Mamiya CS lenses. I also have the 35/2.8, 50/1.7 and 50/3.5 Macro CS lenses. Hadn't thought about converting them ... do you use an adapter or have you actually reworked the mount in some way?


There has been or there still might be a CS to FE/NEX adapter, you might even find a Mamiya E/EF to FE/NEX adapter that could work as the bayonet itself of the Mamiya E/EF is like the CS one. I believe they are hard to get though.
http://forum.mflenses.com/mamiya-cs-and-e-lenses-on-digital-full-frame-t71899.html

However I normally convert my vintage manual lenses to Canon EF mount ones and add an AF confirmation chip to that mount so my Sony A7RII gets the focal length reported from the chip through a Sigma MC11 adapter. Good for IBIS and EXIF. The MC11 also reports the max aperture set in the latest EMF chips, that is quite new. My Olympus OM lenses get an OM<>EF adapter + chip, the same for some M42 lenses I have. Their register distance is more than the 44mm of the Canon EF mount so an adapter is possible. With Minolta MD, Canon FD, Mamiya CS this is not possible as the register distance is shorter than 44mm.


PostPosted: Mon Jul 06, 2020 6:01 pm    Post subject: Re: Mamiya Sekor CS 135/2.8 Aperture Return Spring Reply with quote
Zuikomar wrote:
Hi All

... noticed that the 135/2.8 had oiled aperture blades so I decided to clean them up. This is something I've done many times before on other lenses. Once cleaned and fully operational I reassembled, all now works but not perfectly.
...

Can anyone advise?

Thanks


... get another Sekor CS 2.8/135mm ... they are dirt cheap Wink

S


PostPosted: Wed Jul 08, 2020 9:52 am    Post subject: Reply with quote
Zuikomar wrote:
Interesting. I have a Sony A7ii, which I use with many lenses, but not the Mamiya CS lenses. I also have the 35/2.8, 50/1.7 and 50/3.5 Macro CS lenses. Hadn't thought about converting them ... do you use an adapter or have you actually reworked the mount in some way?

Macro is rare, better not alter it, but resale to collector.
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