Mamiya C330f - focus screen foam replacement advice please

Hi guys,

 

On inspecting the focus screen assembly of my C330f it appears that the foam

is in bad shape, allowing the plastic focus screen to move up and down and

potentially make my photos out of focus. I'll give a description of the

components I'm seeing...

 

There is the focus screen assembly's main outer metal frame, to which the

glass appears to be solidly fixed to at the top.

 

Within that is a smaller metal frame, to which the plastic focus screen is

attached. I can easily remove the plastic screen from the smaller metal frame.

 

The crumbling foam sits between the smaller inner metal frame and the upper-

inside of the main metal frame. It appears to me that when the foam is in good

condition it pushes the inner metal frame and plastic screen assembly down,

further away from the glass.

 

The inner metal frame is fixed to the outer metal frame via four small screws

or lugs. I am assuming that the length of the extension of these four small

screws is vital to syncing the plastic focus screen to the film plane.

 

There is no way to remove the crumbling foam and replace it with new foam

without undoing those four screws and removing the small inner metal frame,

but I'm terrified that if I remove the screws won't be able to screw them back

in at exactly the right length, and my photos will never again be in focus.

 

If anyone who has replaced this foam could give me a step-by-step guide-for-

newbies on how to do it successfully I'd be much appreciative. I'm hoping that

the four screws will actually only screw in to the proper preset point, which

would make things dead easy to fix, but I don't want to take that risk without

expert advice.

 

Thanks in advance,

Carl

I've just had another thought. Is it possible that the four screws I mentioned aren't vital to the proper focussing distance as I first thought?

 

My latest theory is that the inner screen SHOULD in fact be able to move up and down on those four screws, and other lugs that are on the camera body push the inner screen frame up on those four screws to the correct distance to match the film plane, with the foam's purpose simply being to not allow the inner screen frame to move up any higher than where the camera body's lugs place it.

 

It's all starting to make sense! Feel free to shoot me down in flames and educate me if I'm on the wrong track...

You are absolutely correct, its the foam that acts like a spring and keeps the focussing

accurate, this leads to the misunderstood 'mismatched lens pair' non-problem. I've

refoamed my own 2 C330 as well as many others and if the bodies don't make an agreed

sharp shot then the foam needs to be done. Simple. I've done at least 3 bodies where it

was obvious that the focussing screen showed sharp and the neg was obviously off, then

upon refoaming, same test, sharp on screen now gives sharp on negs.

 

I'm not sure if this can be considered a flaw in this camera series, but I learned this repair

from a guy who used to work at the mamiya factory making them. One of my last calls to

this fellow before he closed shop he told me how to do it, since I had sent him lenses and

bodies over the years, I kept sending him my one main C330 body that needed it done

about every 2 years. I now do it about every year or two, after a test or two.

 

The removal of the four screws is what you need to do, releasing the frame and allowing

you to clean out the old foam. Microtools sells replacement foam, but after running out, I

recently refoamed using high-grade weatherstripping foam cut down, seems to do a

slightly better job. I use thin strips, about 2.5-3mm thick. I use smaller strips inbetween

the screw holes, allows the screws to re-seat easier, rather than trying to poke a hole in

the foam with the screw. Its seems to be better to have to squeeze down the frame, the

tension is what does it, so a bit thicker foam is better IMO. As you correctly observed,

when the foam gets sticky it keeps the frame too high, not pushed against the three body

post screws. Don't touch those. Or the mirror. These are set and rarely if ever get shifted.

 

You are on the right track. Change the foam, its easy and keep an eye out for the C330

that your buddy is going to give away because its 'not sharp'. You'll know what to do.

Thanks Christiaan; that's exactly what I wanted to hear. I'll try and track down some 3mm thick foam asap and have a go at the replacement in the near future. Thanks for the tip about the shorter pieces between the screws rather than making a hole for the screws. I'll be sure to do that.

 

Cheers,

 

Carl

Yeah, I'm making it a quest to quell the whole 'mismatched lens pair' thing. Not that it

never happens ever, its just very uncommon. My guess is that the 'mismatched'

phenomenon is usually due to an uneeded adjustment to the lens pair rather than the real

cause of the mirror foam.

 

One that I found seemed to have been 'adjusted' by a well intentioned repair-person, it

was a newer 80mm S version that had an (non OEM) extra shim on the front element group

of the taking lens. I couldn't figure out why this quite pristine lens was just a hair out, on

several bodies, until I found the shim and returned it to its 'mismatched' state, it was then

beautifully tack sharp on all bodies.

 

So the key is to make sure the foam is good first. I have a 135mm that is so good and

sharp, even wide open (center) and that shows if the foam is wearing.

Okay, so after much examination, contemplation, and a pep talk from Christiaan I decided to give it a go. And to aid future generations like myself who come searching here for answers I decided to document the process as I went.

 

To the experienced Mamiya TLR user this problem is probably so basic it hardly bears thinking about, but to the new user who finds that his photos are never sharp and incorrectly blames the lens, mirror, lens mount panel, etc, this could be the fabled 20 cent fix that could save the camera.

 

Let the fun begin...

The underside of the complete focus screen assembly. It is composed of a main frame holding the exterior glass and a smaller inner frame holding the plastic focus screen. Between the two frames is the foam that needs to be replaced.

 

To get our bearings, the knob at the top of the photo attaches it to the rear of the camera body and the open clip at the bottom of the photo attaches it to the front of the camera body.

 

To remove the plastic focus screen undo the clip on the left of the photo. The screen can then slide out from under the clip on the right of the photo.

 

One edge of the offending crumbling foam can just be seen above the "3" sticker in the lower part of the photo.<div></div>

The screen frame with the plastic focus screen removed.

 

The four small screws I have marked on the photo have to be removed in order to remove the inner frame, allowing access to the foam.

 

When the foam is in good condition it acts as a spring between the two metal frames, allowing the inner frame to rise on the four posts (the screws) to a specific point that matches the film plane. The point that the inner frame rises to is specified by three lugs on the camera body (see final photo), which push the inner frame up to the correct point when you install the whole frame assembly on the camera. The springiness off the foam allows the inner frame to rise to the correct point, but won't allow it to rise any higher.<div></div>

Removing the inner frame to gain access to the foam<div></div>

The inner frame (right) removed from the main frame. The crumbling foam is seen in all its glory.<div></div>

The two frames after scraping away the deteriorated foam<div></div>

The black "mat" is a piece of foam rubber I bought from which to cut new pieces for my focus screen. It's 3mm thick and that seems to be a good thickness for this exercise.

 

I bought a 20cm x 20cm square with intentions of also using it to replace the seal around the camera's film door, but I've changed my mind about that. Instead I have decided to use the furrie half of velcro to do that, as the velcro won't be crumbling again in a few years. So for a measly $1.30 I have enough rubber foam here to fix a hundred C330 focus screens (at least!). It's good to start with more than you'll need (although this definitely was overkill!) because I found that I was cutting a piece, trying it on the frame, then cutting another piece slightly wider or narrower for a better fit.<div></div>

The new pieces of foam ready for gluing to the inner frame<div></div>

The finished product.

 

From looking at the original glue marks it appears that the foam was mainly glued to the inner frame (as shown here) but there also appears to be a few minor spots of Mamiya glue on the main frame to glue the foam to it as well. I chose to only glue my foam to the inner frame because it would allow me to slide the inner frame around on the main frame more easily when trying to locate the holes for the four small screws. Besides, when screwed back together it's all held so tightly in place that there is no need to go overboard with the glue.<div></div>

Reattaching the inner frame including the new foam to the main frame.

 

As shown in this photo it's a good idea to push the inner frame down to compress the foam with one hand while screwing down the screw with the other, rather than just screwing down the inner frame and allowing the screw to compress the foam as it tightens. The reason is that those four screws look very delicate, with only the tiniest bit of thread on the tip. I imagine it would be easy to strip the thread if you used the screw to compress the foam.<div></div>

The inner frame is now reattached to the main frame, complete with lovely new foam.<div></div>

After gently cleaning the plastic focus screen and the glass I reattached the plastic screen and the focus screen assembly is once again complete and ready to be reattached to the camera.<div></div>

It's a bit hard to see in this pic, but I have pointed out the three locating lugs on the camera's body that set the required position of the inner frame and plastic screen. When installing the focus screen on the camera these lugs push the inner frame up inside the main frame to the required spot. The new foam doesn't allow the inner frame to rise any higher, even if you turn the camera upside down.

 

Under no circumstances should you fiddle with these lugs on the camera body. Their position is preset at the factory, and if you force them higher or lower the position of the focus screen will no longer match the film plane. As a result your composition will appear to be in focus on the screen, but will be out of focus on the film.

Oops, didn't insert the pic properly. Here it is...<div></div>

And there you have it! Carl's "Dummie?s Guide To Installing New Foam On Your Mamiya TLR Focus Screen".

 

This was my first attempt at it and it was quite a simple and quick process. Most of my time was spent either setting up these snapshots or waiting for the glue to dry before reassembling the frame. With more experience there wouldn't be as much trial and error in cutting the foam pieces, and I'm sure I'd do it a bit neater next time too, but I'm very happy with the result. When I reattached the screen to the camera I could feel a nice firm compression on the inner frame from the lugs on the camera, which made a great change from the rattling around the inner frame used to do.

 

If anyone has any tips with easier/better methods of doing this please feel free to add them to this thread.

 

Cheers,

Carl

Perfect! An excellent tutorial on how to do it. It is Very close to how I do it, but the

differences are minor. Good observations on the 4 screw heads being easy to strip.

Hopefully now we can all drop the whole mismatched lens pair thing and somebody will refer

or search out the thread and the top notch repair advice. Well done Carl!

Thanks for putting the instructions together Carl. I'm going to try to get to my Mamiya tlrs this weekend. Thanks, TD

This posting inspired me to go replace the foam on the focus screen for my C220F a few

days ago. It seems much easier for the C220 than your C330.

 

I just pulled off the finder hood. slid a little slide and could pull out the screen with no

problem. My foam was definitely gunky as hell and luckily I had foam left over from doing

the film back several years ago. It also allowed me to clean off the mirror very gently...I never

knew I could do that so easily! My focus screen has never been so clear and bright!

Ah, that's interesting. Correct me if I'm wrong, but I think one difference between the C330(inc f&s) and the C220 is that the C330 was designed with interchangable screens but the C220 wasn't. So perhaps my screen assembly is more complicated because it was meant to be easily removable and replaced as a complete unit. Since yours was designed to just remain on the camera it probably didn't need the extra bits that would keep it together as a unit off the camera. Happy to hear it all went well.

 

Pulling the screen assembly apart and doing repairs was a big step for me. I'm still too paranoid to touch the mirror!

<p>HI Carl,<br>

Thank you indeed for posting the steps you took. In response to them I re-foamed the viewing assembly for my C330f. It clearly needed to be done since sharp focusing below f5.6 wasn't possible, however it didn't solve the discrepancy between the viewing focus and the image on a focus screen I constructed for the film plane. Before I detail my problems, I'll add some advice for others changing their viewing assembly foam.</p>

<p>I was able to predict before changing the foam that it wouldn't have made a difference by dabbing some slow drying ink onto the 3 posts in the C330f's body then putting the screen assembly back onto the camera, removing it and seeing 3 ink dots transferred to the underside of the screen. This was despite my foam being in poor condition.</p>

<p>For others reading this thread, the two problems causing my discrepancy were as follows:</p>

 

<ol>

<li>The top of the lens plate/board was able to rock back and forth by about 1mm because the stiff retaining wire didn't press on it when latched as it should. I solved that problem by inserting a small piece of sheet metal (LxWxH about 2mm x 3mm x 1mm) to take up the slack.</li>

<li>I had previously swapped the front of the viewing and taking lens with each other. This was because I had a small amount of fungus on the taking lens. After considering this might have been the problem I noticed that both lens bodies had different thickness shims between them and the lens plate, also the filter thread of the viewing lens was about 0.5mm further forward than that on the taking lens. After I swapped them back again the focus was identical (to within limits of repeatability).</li>

</ol>

<p>The amount the focus was out was a distance of 0.6mm linear travel of the bellows and about 2.2mm circumferential rotation of the focus knob.</p>