Mamiya C33 TLR Repair - Part 3 (Sekor 80mm f2.8 Twin Lens)

In the last part of the 3-partite re-commissioning journey of my Mamiya C33 TLR, I work on the Sekor 80mm f2.8 lens in Seikosha shutter. Is this the dreaded silver-fronted one that every repairs person hates? I do not know. You tell me.

The problem was simple: aperture was completely jammed in place. The lever wouldn't even budge the slightest. I did not expect this to be oil on blades because it was completely frozen in place. I expected another mechanical problem, dirt in gears or something, so on to disassembly.

First of course you need to take the lens off the main plate. Using a lens spanner or a vernier caliper, turn the rear holding ring to unscrew it and pull the lens out. You cannot simply remove the bottom taking lens on its own. You have to start with the four screws around the viewing lens in order to free the sync-port which is connected to the shutter mechanism in the viewing lens.

Taking lens assembly with sync port

Then remove the yellow ring from the back to reveal the three little screws under it. These screws hold the external aperture arm. Get that out of the way.

The peripheral screws hold the whole assembly together. Take those out and brace yourself for disaster. Pull the front and back apart and LO! there are your shutter blades, all over the place!

These springs will also pop on the sides. There are four of them. If you opened the mechanism from the back like I did, do not worry about them as they will not go anywhere.

There are five blades in the shutter. I read somewhere that there is a fifth retaining blade (half-blade) but I only found five in mine. Maybe the sixth was already stuck to one of them? Maybe different models?

There was nothing to fix in the shutter mechanism or blades as it worked fine. So I left them aside on a white paper along with the front part of the mechanism, and headed towards the rear part, which is the aperture. This little arm below is what controls the aperture but it was completely jammed in place.

On the inside, this is the aperture. Remove the screws holding the black thing from the metal housing.

On the other side of this ring, the aperture blades were completely stuck as if they were glued. The dreaded oil was gummed up

To clean that up, I soaked the blades in isopropyl alcohol, and used cotton q-tips to clean them off, making sure they are layed flat on a hard surface to avoid irreversible accidents. These blades are extremely thin layers of metal (iron, they can be picked up with a magnet) and bending them the slightest is not an option.

This is the other wide of the aperture retaining ring. This is the part which turns when you slide the aperture arm. This stays in the metal housing, no need to remove it.

Putting the blades back in place is a very tricky business and you should get it quite right. Layer the leafs/blades as they should be, carefully install the upper retaining ring or tracks ring, make sure everything is in place, be very careful, double check, install the screws.

It should be very smooth with almost no resistance. Do not worry about it. Resistance will be back when you assemble the whole thing. But before you can put the front and rear part together, you need to put the shutter blades in place.

Putting the shutter blades in place is similar to assembling the aperture, but please note the side to which you put blades. I took the following pictures but I think I reversed the direction of the blades afterwards. Please note the pictures may be wrong, so I share them for illustration purposes only. Also for showing off.

The last part is to put the front and back parts of the entire lens together. You need to make sure the shutter blades stay in place and slide safely into the track ring as you close them in together. Keep the front part with the shutter blades flat on the table and mount the rear part upside down on top of it. Use a screwdriver or something to push the springs into the mechanism before you close it well, and fit the four screws.

This finishes the difficult part of the job and all that is left is to put the lens back together. The sync type (X and M) arm/ring is the trickier of the two. See if the following pictures can help you figure out how it should go. See that part part which bends inside the assembly and goes just behind the shutter release? You'll need tweezers or a screwdriver or anything similar to guide a small metal 'petal' into that bending part. This gives this arm its "click" when you switch the sync type.

See the sync arrow is pointing towards X. This is the best indicator as to how this ring should go.

Aperture arm, the last screws in the assembly and then the yellow ring back in place.

With the aperture arm and the yellow ring back in place, all screws fitted, the whole assembly is ready to do onto the main twin lens plate.

Fit the taking lens first. Very easy to orient it according to the little hole in the back. It is the same stud that holds the big yellow ring above. Simply fit correctly and screw on the rear ring.

Then fit the sync port. Do not forget the metal plate that connects the lower rear screw to the sync-electrode.

The viewing lens should be fine long as you keep the shims as they are.

Align the upper stud with the slit, and screw on the rear ring.

If everything goes well, you have a working twin lens.

In fact, the calibration process that I talked about in the last post was done after this aperture cleanup was finished. I wanted to make sure the two lenses were perfectly aligned. It is difficult to align them wrong, just don't strip your rear holding rings.

And because it all went well in my case, you get two more extra pictures.

Mamiya C33 TLR Repair - Part 2

In Part 1, I showed you the body's mechanics. In this part, I will show you the focusing screen and what I did to calibrate it.

The camera came with a waist level finder and an eye-level porrofinder. Both were good except that the flaps on the WLF needed to be pulled by hand every time. That was alright.

The problem though was that the focusing screen itself seemed dirty. I know that in a DSLR you should not try to clean a focusing screen, in fact, you can't, but I wanted to give this a shot anyway.

I do not recommend you attempt to clean your focusing screen, and you will see that I could not do anything to it anyway, but the pictures below may come in handy for anyone wanting to know how this thing is constructed, in case you want to replace your parts or something.

In this picture, you can see the smudges that made me want to clean the screen. They looked like moisture formulations and I was worried about possible fungus growth.

To remove the focusing screen first you need to remove the finder. You will find that there are 5 aluminium screws holding it in place. Remove these very carefully and try to pull the metal mount vertically upwards. The screws hold the shims that you need so much to keep the screen at the precise right distance from the lens. DO NOT LOSE THOSE, and do not drop them when you remove the metal plate. Especially if you have the rubbish bin right between your legs while working.

This is what would happen if you do. Can you find the shim?

It's in the lowest end of the picture near the abc sticker.

There are three long black paper shims, four small round shims (two yellow, and two thicker white ones), and two very thick (about 1mm thick?) shims.

And this is how the ground glass is mounted on the aluminium plate. Notice the lack of any light seals in this model. I heard the C330 has light seals that function as cushions which push the glass up. In this model you only have the two retainers holding the glass in place, and they are held in place with two screws each. The glass is also glued to the aluminium so I did not bother disassemble any further.

But mainly because I found out that the focusing screen is in fact two layers stuck to each other. The smooth side of each layer is facing outwards so it is safe to wipe clean, but as the formulations are in the middle between the two, separating them for cleaning meant certain irreversible destruction.

In case you want to clean or replace your mirror (if you can source and cut a similar mirror, that is), there is one screw holding the mirror in place and you can access it from the front through the opening of the viewing lens.

Loosen this screw and you can pull the mirror out.

Here you can see the screw again without the mirror in place.

And this is the top of the camera without the mirror. There are some metallic plates that will push the mirror against the edges to hold it firm in place.

If you do not need to mess around with the focusing screen, keep it in place. If you had to clean or change the focusing screen, put everything back in place and pay special attention to the shims. When I took mine off, the shims fell off and I had to figure out where to put each par. In the end, I put the three paper shims in the front, and each screw in the back got a single one of each of the three types of shims. When I forgot one thick shim, the focusing calibration was visibly wrong.

So now that everything is back in place, you need to make sure your focus is right, and to do that, you need to be able to look at both the focus plane, and the film plane.

On this model, you can remove the back cover completely by undoing the locks you can see in the following picture.

Then in order to be able to see what the film will actually record, you need to put another 'focusing screen' where the film goes. For that, semi-transparent paper lamination will do. It's quite thin but only hard enough to maintain its flatness. I used double sided tape to fit this cross-shaped piece of lamination (which is a leftover from this post, if you remember) right where the film should go.

Calibrating the focusing screen is simply a matter of putting the right shims in the right place. You need to have the focusing glass at the same distance from the viewing lens, as the film plane is from the taking lens.

It is very interesting the way you can see the image forming on this plane when you open the shutter. See the video in the previous blog post. However, I decided to a cut a new square piece to cover the entire area because I needed it to be completely flat. Flatness is of absolute importance.

Fix the camera on a firm tripod (Manfrotto Magic Arm in my case) and focus it at any given object. I normally calibrate either for infinity or at the minimum focusing distance of a lens depending on the requirements of the job, but due to the nature of the camera and other limitations, I simply focused at the clearest object I could see which did not cause the parallax correction arm to appear, which was the chrome ring on a lens on my window sill. The shutter's bulb mode will be essential at this stage.

To verify you're doing it right, you now need to look very closely at both images. A large-format magnifying loupe can be your friend, but if you're like me (on a budget) and don't have one, you can, like me, use the front element of an old, broken, Sigma 70-210mm lens along with its own hood. Just insert the element in the hood until it is firm in place. Now you have a magnifying loupe which you can use on both the focusing screen, and the film-plane's lamination screen.

May take a while to get it right, and will take removing the upper focusing screen and putting it back several times, but once you do it right you'll be happy.

Test for the focus at the centre and also at all corners of the frame. Also test focus match at all distances: from infinity down to close-enough for parralax not to interfere. If I had one of those mounts that correct the placement of TLR lenses (y'know, they shift the entire body so that the taking lens is exactly where the viewing lens was), then I would also test it for macro focusing.

Finally, when I was happy that the focusing screen is calibrated right, and before putting the back cover back, it was the right time to replace the light seals. As you can see, the seals were completely deteriorated on my camera. In some cases it may not have an effect as some cameras still prevent light even without foam seals, but I did not want to take my chances. 

First off, the old deteriorating seals need to be removed. Cotton pods, q-tips, wooden sticks (broken matchsticks?) and lots of proper solvents should be used until the thing is pretty clean. I used %99.8 Isopropyl Alcohol.

Then I simply cut the right size and thickness of foam from a big piece that I have. You can probably buy a seal kit pre-cut for your camera model, but it works out a lot cheaper if you do many cameras to buy bigger pieces and cut to your desire.

This camera requires one wide 1cm piece and three long 2mm pieces of 2mm thick open-cell foam. I used self-adhesive ones but you can use latex adhesive to stick a non-sticky foam.