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Adjusting infinity on Mamiya Sekor SX 135/2.8
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PostPosted: Fri Dec 12, 2008 11:19 pm    Post subject: Adjusting infinity on Mamiya Sekor SX 135/2.8 Reply with quote

Just a quick pictorial. It might help someone, I don't know... Smile

After this you can slide the outer focusing barrel off the central barrel. Unscrew the holding screws as far as you dare, but be careful not to go too far - they are quite easy to loose! Smile When you have removed the outer barrel, the lens will look like this:

The aluminium part you now see is actually in two parts, the one towards the aperture-ring is the end-stopper for the focusing action. As the picture says, we are now at MFD. The stopping ring rests on one of the pins sticking out from the lens base.

Here it is, turned almost a full turn the other way - at infinity stop. It now stops on the other pin, from the other direction.

Now you loosen the four holding screws on the stopping ring. The ring and its holding screws is fixed by a small amount of soft glue, you might need to fix the body of the lens with something (a square-jaw vise is the best) and gently knock one of the stopping surfaces with something reasonably hard - like a medium flat screwdriver. It will rotate quite easily once loosened.

With the locking mechanism disabled you can pull the focusing mechanism quite a bit further towards infinity before hitting hard stop.
The first parts to mechanically ground are the two pins that the stopping ring works against. They're to tall - unnecessarily tall now - so I filed (Dremel'd) them down about a mm or perhaps a bit more. Now the focusing action can be rotated until the central helicoid barrel grounds on the main lens barrel. This is as far as it will go without dismantling the lens and putting the central barrel on the lathe... Hopefully it will be enough. I needed 1.7mm, and I think that I'm close.

Now all that's left is to turn the focusing action as far IN as is mechanically possible, and re-thighten the locking ring with the infinity stop just touching the correct pin. That should look like the picture above the previous picture.

Remount the outer barrel, align its infinity mark roughly against the 0-line on the lens body, tighten holding screws. use the thinnest M42-adapter you can find, and the Nikon F-mount Mamiya 135/2.8 is ready to go... Remember to jam the aperture pin in some way, or open the lens-mount and reroute the spring - otherwise the aperture mechanism won't work, just as in any other M auto lens...

This lens was convertible to Nikon-F without having to do any non-reversible or special tool surgery. I wouldn't have minded doing that, but not having to is always easier. I'm 1/10 mm away from reaching infinity in cold weather now, but I will solve that by taking .2 off from the adapter. That will have to wait until monday - I don't have a lathe at home... Smile

PostPosted: Fri Dec 12, 2008 11:27 pm    Post subject: Reply with quote

Many thanks for this nice tutorial!

PostPosted: Fri Dec 12, 2008 11:33 pm    Post subject: Reply with quote

THANK YOU! ^Smile^

PostPosted: Sat Dec 13, 2008 9:28 am    Post subject: Reply with quote

Great pictorial, thank you very much!

PostPosted: Sat Dec 13, 2008 9:48 am    Post subject: Reply with quote

Many thanks. I enjoy this sort of thing very much.

PostPosted: Sat Dec 13, 2008 11:53 am    Post subject: Reply with quote


Many thanks for the tutorial, i really like this kind posts Very Happy

Hoping to see more ...

Best regards

PostPosted: Mon Dec 15, 2008 4:23 pm    Post subject: Reply with quote

Hello, nice tutorial.

I also have a mamiya sekor 135mm f2.8, it is like new. The only difference with yours is the focusing barrel, it is all metallic.

I am completely new to manual focus, it might be that I ask you a silly question, but Illl do it anyway.

My camera is canon but i think this should apply to both cases.

I see in your second picture that the aperture ring is exactly like mine. It has a slight edge that goes into the territory of the screw. When I attach the adapter I have no problem but when I mount it into the camera that edge of the aperture ring touches de body not letting it screw to the end and also locking the aperture ring against the body.

When I see your third picture I see the adapter but it is only screwed to the point where it is at the same level of that edge, so when you mount it into the camera it wont touch. How do you do this?

I assume that this is part of the conversion and that mount, not completely screwed, is what makes mandatory to adjust the infinite focus, is that right?

Now I am at work and I dont remember whether in my focusing barrel has screws to adjust or not, hope they are there, i cant cut anything cause it is all metallic.

I hope I have explained my problem in an understandable way Very Happy


PostPosted: Tue Dec 16, 2008 4:22 am    Post subject: Reply with quote

@Atwim: I have "trimmed" the outer diameter of my used adapter a bit - it now fits INSIDE the protruding ring of the aperture ring. Since you will be using the lens on a Canon EF-mount, you shouldn't have to do this - a 0.5mm shim between the adapter and the lens would do the trick.

You would still be able to tighten the adapter to the lens tightly enough, and I don't think the shim has to be thick enough to make the combination overshoot the infinity focus...

[edit] - I've unscrewed the adapter, and just laid it up side down on top of the lens. I see now that the picture isn't totally clear on that part... Smile

PostPosted: Tue Dec 16, 2008 5:44 pm    Post subject: Reply with quote

Thank you for the answer, as soon as I have some time I will try it.
Is there any material I should use for that shim better than others? A piede of plastic, metal, wood...?

PostPosted: Tue Dec 16, 2008 6:02 pm    Post subject: Reply with quote

Most plastics may have a friction coefficient that's insufficient to keep the lens tight on to the adapter, but metal is harder to cut.... At first, I'd try with the densest (most "compact") cardboard that I could find, and if infinity focus is ok and the cardboard doesn't feel stable enough for extended use, I'd try to get a cupper/brass shim...

If you can't reach infinity with the shim, I'd remove the aperture ring and trim down the "lip" that protrudes... This is probably easier than modifying the adapter if you have to do the work without having access to a lathe Smile

PostPosted: Mon Jul 30, 2012 3:39 pm    Post subject: Reply with quote

Great tut! *clap!clap!clap!* you just helped me getting my Mamiya to infinite! thanks a bunch! as a side note, the soft glue wasn't present on the ring, just a little on the screws - it was actually pretty easy to fix it up!

Thanks again!!

PostPosted: Thu Nov 24, 2022 5:18 pm    Post subject: Reply with quote

An old post, but some time ago I've got a SX 135mm 2.8 iris blocked , today I've cleaned it , and after putting it together, lens only will focus to little more than 20 meters . I wonder if I've out together something wrong , as I haven't touched focusing helical at all. Maybe when I've loosen front group ,the helical might have moved together? Or fixing the mount on the lens ? The aperture ring works nice ,also focusing group, only issue us not reaching further than 20meters.

PostPosted: Thu Nov 24, 2022 7:25 pm    Post subject: Reply with quote

I can confirm that assembly is faulty , so I need to recheck everything. The iris was working nice , but now the pin stay half pressed when lens is off. I'm using a special adapter that shouldn't give any trouble for the pin. On the other side , for the little shots I took , i am surprised of the sharpness this lens has got wide open.

PostPosted: Fri Nov 25, 2022 4:52 pm    Post subject: Reply with quote

Ok, I've opened it and put a little wire rubber (3mm long) along the pin, and works good,but not fir long.
For whatever reason , the pin is falling inside the lens , that's the reason lens wasn't focusing at infinity. For the same reason (i suspect) , having to remove the mount with the pin inside (had to use bit of force at some point), now the lever of the diaphragm,whener actioned inside the lens (without the mount and aperture ring installed) would only open lens up to 3.5 +-. So the iris won't go open all the way to 2.8 wide open.
When I've got the lens, as I've mentioned before , the aperture was stuck. I've cleaned the iris soaking it with alcohol and blades seem clean and working !at least at the point that everything has messed up). I suspect, the ring that hold the irus , for whatever reason might have moved and that .ight be the reason that blades won't open totally ,even if the lever will go to wide open . Regarding the pin, i suspect something might have got loosen and could be glueing the pin in its hole.
Can anyone give me a hint regarding these issues? Thanks

PostPosted: Sat Nov 26, 2022 3:24 pm    Post subject: Reply with quote

Update. I've figured out that, the lever that's moved by the aperture ring, is seated on a plate with 2 screws , releasing those 2 screws will allow to adjust the aperture stop if the blades, so piece of cake. For now, I've glued the pin with the rubber on it's place so, hopefully will got it working soon. The first shots I've taken , I'm really amazed by the sharpness wide open of this lens.


PostPosted: Sat Nov 26, 2022 4:49 pm    Post subject: Reply with quote

Same issue as before, with the mount removed the two levers that moves the aperture and stop down , work well, closing and opening blades correctly.
Once I out the mount on, the blades are closing just as it would be a F4, the blades a bit closed ,so from f4 ,when I'm opening the aperture ,the iris won't open more the blades . The f16 in this lens looks like f22 sonnar c/y. For whatever reason , the iris is not working all together properly with the aperture lens.
At least, now I figured out how to open fast this lens , making it work properly ,is another issue.