detach seiko shutter from Mamiya Press 100mm 2.8

Discussion in 'Medium Format' started by stan_wagter, Jun 3, 2021.

  1. Hi all,
    I have to replace the 'Mamiya Diaphragm Aperture Control Lever Knob'...yes, on ebay sombody is selling it, due to broken attachment. Althought the front part of the lens unscrews easy form the sutter, I can't get tthe shutter fro the rear end, and that's (I hope) where i have to be to open up the shutter. Any experience here? Can you just enscrew it, or do I have to detach the focus mechanisme?
  2. Congrats on owning the marvelous (and rather scarce) 100mm f/2.8! Always wanted one myself, but they're hard to find in the desirable later version you have. All my Press lenses are the older silver-face version; with these, the shutter barrel completely detaches from the focus helicoid after you unscrew the rear element and remove a retaining ring securing the shutter barrel to the helicoid. Note the flash sync wire can be a real PITA to deal with when the barrel is detached from the focus mount: re-soldering is often necessary.

    While I don't own this specific Press lens, I do own many similarly constructed Mamiya TLR lenses of the same black-barrel era with side-operated aperture lever and shutter rings (some parts like the plastic aperture handle are the same for both the Press and TLR lenses). Going by your partial disassembly photo, I think it might be easier to try and tackle this problem from the front: since this lens uses the same plastic TLR aperture handle with three securing screws, your access issue to the lower single screw hole is might best be solved from the top of the lens.

    In photos I've seen of the intact late-model 100mm f/2.8, the aperture handle is fitted exactly as on the TLR series lenses. However, unlike the TLR lenses (which keep all three screws exposed) the lower handle screw is covered by the shutter speed ring in this Press lens. Your Press lens shutter barrel appears to have the same nestled ring construction as the Mamiya black TLR lenses: sometimes what seems to be a solid ring is actually two or three nested rings held together by top-facing screws. Removing those screws allows pulling off additional segments of the barrel, which may allow you to access the lower attachment screw hole for the handle.

    I think you want to remove the top facing screws visible in your photo: this should let you lift off the aperture control ring and perhaps the shutter speed control ring, and figure out how the whole assembly needs to be re-nested after installing the replacement handle. Go slowly and watch out for any hidden leaf springs or ball bearings between the rings that create the click stops. I posted some pics detailing disassembly of the similar TLR shutter/aperture controls on this other thread: it might help you get where you need to in this Press barrel. Good luck!
    Last edited: Jun 4, 2021
    NHSN likes this.
  3. Argh, forget what I said about going in from the top: I thought the lower aperture handle screw was blocked by the shutter speed ring, but looking closely at other photos I see now it is blocked by the metal shell cup the shutter barrel fits into on the focus helicoid.

    So your first instinct is probably correct: unscrew the rear element, use a spanner to unscrew the retaining ring you'll find underneath it, and pull the entire shutter barrel out from the front. This will let you install the lower aperture handle screw, which will be covered once more after you replace the shutter barrel in the shell cup of the helicoid.

    Apologies for not catching this in time to edit my earlier post. :(
    peter_fowler likes this.
  4. Thank you Orsetto, great to have such a detailed reply.
    Yes, I already lost a ball inicator !! see image...
    Seiko-Shutter-fragment 3.jpg

    What I still don't understand is the process of unsreer ther rear element. You mention this: 'the shutter barrel completely detaches from the focus helicoid after you unscrew the rear element and remove a retaining ring securing the shutter barrel to the helicoid.'In order to enscrew the rear element, I first have to remove the focusunit. as far as I can tell.
    I put in some extra images:
    mamiya1.jpg mamiya2.jpg
  5. Here's a link to your image, with a few markings: mamiya lens retaining ring.jpg

    The slots in the red circles are in the shutter's retaining ring. Use a spanner to unscrew the ring.
  6. The Press lenses are somewhat difficult to take apart without special tools, and even with the tools it can be a clumsy, tricky and risky process. Your 100 f/2.8 is very rare to find now in good condition: if you live in a place where there are professional camera repair technicians, I would strongly recommend paying for professional service for this particular lens. If you haven't successfully worked on a Press lens before, there is great risk of damaging the rear element glass during disassembly and reassembly. With this warning said:

    You never, ever want to take apart the focusing helicoid unless the focusing itself is broken. The Press lenses are designed very much like the Mamiya TLR lenses or view camera lenses: the shutter barrel is self-contained and is simply bolted on to a mount for the camera. With the TLR and view camera, that mount is a simple plate with no helicoid: the Press lens adds a focus helicoid but the assembly design is the same. IOW, the Press lenses are assembled in this manner from front to back:

    Front element screws into front threads of shutter barrel.

    Shutter barrel has external rear threads that poke thru a hole in the front of the helicoid (inside the metal cup).

    A retaining ring screws over the shutter barrel rear external threads, forming a sandwich with the helicoid front plate: this secures the shutter barrel to the focus mount.

    Lastly, the rear element screws into the internal rear threads of the shutter barrel (covering the retaining ring that holds the shutter barrel in place).

    The problem is the protective metal cup that the shutter barrel fits into blocks access to certain things like the aperture handle lower screw. This metal cup cannot be removed, so the only way to reach areas of the shutter barrel that it blocks is to unscrew the rear element cell, unscrew the retaining ring that holds the shutter barrel in place, then pull the shutter barrel away from the focus mount and out of the cup.

    This is easy to describe but difficult to do, because the rear element and shutter barrel retaining ring are buried deep inside the rear of the focus mount. In some lenses like yours, there is also an additional squarish thin metal light baffle (or several baffles) impeding access for tools. These baffles are held in place with spots of lacquer at their edges: this needs to be dissolved or gently chipped away, then the baffles carefully wiggled out.

    With the baffle removed, you have a bit more room to maneuver your tools, but space is still very tight. To unscrew the rear element cell (and the shutter barrel retaining ring underneath it) you need a much longer than usual spanner wrench made for lens work. The two blade pins of the spanner fit into the slots Dan Fromm circled in red. Unscrew the rear element cell with the spanner, then the retaining ring revealed underneath, and the shutter barrel will simply lift out of the focus mount front cup (actually it will fall out if facing downward, so work over a soft towel). The shutter barrel has a short wire connecting it to the flash socket: this is a pain to re-solder, so do not detach it for this job: you should be able to install the new aperture handle with the flash wire still attached.

    The great challenge is finding a spanner tool long enough and strong enough to reach deep inside the rear focus mount to unscrew the rear element and shutter barrel retaining ring. The genuine Mamiya tool is impossible to get nowadays, so most of us make do with a metal compass normally used for engineering drawings. The pointed tips of the two arms need to be filed to a flatter shape to fit into the rear element rim slots and the retaining ring slots. Maneuverability and grip are extremely difficult once you poke the compass arms inside the lens barrel: the tips will almost certainly slip more than once before the tightly screwed in rear element begins to turn. This is where the enormous risk of scratching the rear element lies: you must be very patient and careful, and cover the rear element glass with non-destructive tape or putty to protect it before you start.
    Last edited: Jun 5, 2021
  7. Looking again at your pics, it seems the square light baffle Mamiya put in the 100mm f/2.8 is a more substantial part of the outer rear mount that may not be removable: if so, don't try. In other Press lenses these baffles are thinner and located inside the focus mount closer to the glass, held in place by lacquer. Those are more problematic and need to be removed, but the outer fixed baffle of your 100mm might not get in the way of tools nearly as much. If it doesn't seem to be easily removable, leave it in place.
  8. See pics below for the needed tools. The smaller is a standard spanner wrench typically used on lens cells and retainer rings, the larger is a compass long enough to fit inside deeper challenges like some of the Press lenses.

    My older slower 100mm f/3.5 press lens (shown) doesn't seem to be as deep inside as your f/2.8, so I'm able to use the smaller standard spanner wrench to unscrew the rear element bloc and the shutter barrel retaining ring under it. Note the slower 100mm f/3.5 has a much smaller rear element cell: so small, the spanner wrench can actually fit over it to reach the larger diameter shutter barrel retaining ring below it. The larger rear element cell of your 100mm f/2.8 blocks access to the retaining ring, so would definitely need to be removed before you could reach it.

    Make sure you have the focus ring set for infinity distance, this brings the rear element as close to the rear opening of the lens mount as possible. In this position you might be able to use the smaller, standard spanner tool. This is much easier to handle and control than the makeshift compass, but if you can't reach the rings with the normal tool you'll need the compass.

    _Spanner & Compass.jpg
    _Spanner Inside 100mm Press.jpg
    Last edited: Jun 5, 2021

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