Mamiya tlr focusing problem

[pbromaghin]

Please bear with me as this is complicated and difficult to explain clearly.

The film plane does not agree with the ground glass on my C-33. When focused at 10 feet with the 80mm, the picture comes out focused at around 8 feet. The repair guy says the lens mounting bracket is bent so that the taking lens is just slightly farther from the film than the viewing lens is from the ground glass. He points to it not being exactly parallel with the main body when cranked all the way in. The difference from top to bottom of the mount is about 1 mm. However, when visiting Central Camera in Chicago I saw this exact difference on the other Mamiyas on their shelf. The sales guy said it was more likely that the lens assembly was out of line and suggested that I do a test with the other lenses.

So I marked the front of my house with tape at 6" intervals, set the tripod up at distances of 5, 10 and 15 feet at 45 degrees from the wall, and took one shot at each distance with the 80mm, 105mm, 135mm and 180mm with the apertures at maximum opening. All shots showed the plane of focus to be some distance in front of the intended focus point. In each photo, the in-focus area is a small strip going straight from top to bottom.

If the mounting bracket were indeed out of true then both lenses would point slightly upward, and wouldn't that be the same as a slight backward tilt in the front standard of a view camera? If so, I would expect the area of focus to move diagonally on the negatives, rather than straight up and down, due to the wall being at a 45 degree angle.

Might I be lucky and only need the ground glass position to be adjusted with slightly thicker shims?

 

[John Koehrer]

Easy to check,
Use a ground glass at the film plane & set the focus, then adjust the screen to match.
I haven't seen one in the flesh for years but most TLR's use either shims or a spring under the screen to allow adjustment with the corner screws.

 

[paul ron]

John has hit it right on the head. Focus the taking lens to film plane.... The tune your viewing lens n screen.

It's been a long time since I worked in a Mamiya TLR... either the viewing lens shims or the screen adjusts. I'll have dig my camera out to see it, but I don't have a c-33, I have the C-330 pro-s... I know some of these cameras had affixed screens.

BTW there is a guy Graham Paterson is the expert if you Google him his site is very useful for these kind of problems.

 

[polyglot]

Do you have just the one lens? That makes it difficult to determine if the lens or camera is the problem. It's pretty hard for the lens to be wrong though because the lens board is just a metal board, it should be flat and the two lenses should be mounted in it identically. As you say, if the plane of focus is vertical then the front standard is probably not bent.

I would expect that you just need more shims under the focus screen. I got a C220 recently with a similar but less severe issue - focusing about 0.8m short at 6m. A bit of extra shimming has it nicely aligned now and shooting about as sharp as I think that lens is capable of.

Edit: finding appropriate shims is annoying unless you have a local hobby store with shim stock handy. I cut a strip out of a baked-bean can, measured it to be 0.2mm thick, drilled a bunch of holes in it and then cut my shims out with tinsnips.

 

[jochen]

Hello,
is it possible with the C 33 to put in the viewing screen upside down?

 

[micwag2]

Hello,
is it possible with the C 33 to put in the viewing screen upside down?

This is a good point. The focus screen is only ground on one side. If it is in backwards then your focus will be off. Has the camera been apart for cleaning?

 

[Rick A]

You may want to check to see if the rear elements of the lenses are screwed in properly.

 

[paul ron]

Ah focusing screen may be upside down... Good point.

The dull side should be down.

It would be nice to check another lens on there. It is also possible your lens may be a DIY fixer upper n shims were removed or viewing n taking lenses were swapped. Look for tool marks and the beauty ring will also say VIEWING N TAKING lens but that could have been swapped as well.

But so far it seems everyone has given you every possabe senerio.

Try another lens before adjusting anything.

 

[Jojje]

Propably the method for adjusting the focusing in manual for C220 will work: http://www.cameramanuals.org/mamiya_pdf/mamiya_c220_pro_repair.pdf
I've had some focusing issues with my Mamiya C220 and Mamiyaflex C2 cameras. The plastic focusing screen of C220 was slightly curved. Made adjusting shims (washers) with small punches out of a beer can.

 

[pbromaghin]

Upside down focus screen... I'll have to check that.

It has also been suggested to do a lens mount parallelism check and also to measure more exactly the difference in the subject focus distance and do the math to get the difference in image focus distance.

I have strongly suspected all along that it's a shim problem. I did test with 4 different lenses at 3 distances and every one looked exactly alike so it seems to confirm this. Is there anything else that anybody thinks I should look for in the negs?

Mike Butkus has the owners guide, but does anybody have a link to a C33 repair manual?

 

[pbromaghin]

I just thought of something. An upside down focus screen would produce exactly the opposite problem than the one I am having. The film plane would be closer to the lens so the subject in focus would be beyond where the taking lens is focused.

 

[PeterB]

Hi pbromaghin. Check out my comprehensive suggestions in the last two posts in the thread beginning here (there was a url link here which no longer exists). They should assist anybody attempting to fix/calibrate their TLR's focus (I used a Mamiya C330).

regards
Peter

 

[pbromaghin]

Hi pbromaghin. Check out my comprehensive suggestions in the last two posts in the thread beginning here (there was a url link here which no longer exists). They should assist anybody attempting to fix/calibrate their TLR's focus (I used a Mamiya C330).

regards
Peter

Thanks, Peter. Reading that made me feel your pain. This corresponds closely with other advice I have gotten outside this thread. I'm going to show your last 2 posts to my repair guy, It's starting to look like a good idea to buy a repair manual, too.

 

[Christiaan Phleger]

yeah it sounds like a classic case of the foam underneath the focussing screen deteriorating. I'm pretty sure my comments are in PeterB's thread. I would suggest starting with examining the foam of the screen First before messing with anything else.

 

[pbromaghin]

yeah it sounds like a classic case of the foam underneath the focussing screen deteriorating.

Oooooh. I hadn't thought of it that way. Makes a lot of sense.

 

[pbromaghin]

Revisiting this

My repair guy just can't be convinced there is a problem. I even showed him a roll that I shot to diagnose the problem. Does anybody see any big hole in this procedure?:

Taking a clue from PeterB above, I set the camera on a tripod at 45 degrees from the brick front of my house with the sun at an angle to create lots of texture. I put several lengths of tape on the wall, vertically at 6-inch intervals. I then took 12 shots, 1 each for the f/80, f/105, f/135 and f/180 at 5 feet, 10 feet and 15 feet, all at maximum aperture.

After developing the roll, I examined it with a loupe on the light box and guestimated the difference between the target and the actual focus plane (a2 + b2 = c2). I then plugged these guestimates into the focal formula 1/lens focal length = 1/subject distance + 1/image distance. I figured that with 12 data points, even if some of the m are off, the aggregate will be better than what I have now.

I haven't calculated all the data points yet, but so far the average appears that I need a 1 mm shim under the ground glass. I plan to order a C-33 repair manual this week on eBay.

 

[Xmas]

https://www.flickr.com/groups/mamiyatwinlens/discuss/72157602889319011/

inspect the foam...

 

[pbromaghin]

Nice link. Thank you, Xmas. I haven't opened the camera up myself yet. I am reluctant to do so until I have the repair manual in hand.

 

[Xmas]

Undo the knob at rear of screen hood and lift off the screen hood.
As documented in user manual...

 

[grahamp]

Just to clarify: How did you measure the 5, 10, and 15ft distances? Measure from the central subject marker to a point on the camera, or using the focus scale? I am assuming the physical tape measure method, otherwise you have a secondary variable in the mix.

 

[pbromaghin]

Undo the knob at rear of screen hood and lift off the screen hood.
As documented in user manual...

There's more to it than that That just gets you to the focus screen. You're safe up to here, but I won't go beyond this without the manual because this is when the little parts start bouncing around the floor.

Edit to add: Also, I have read that the C-33 and C-330 ground glass mounts are quite different, incompatible even, and I wonder if the C-33 even has the foam. We shall see.

 

[pbromaghin]

Just to clarify: How did you measure the 5, 10, and 15ft distances? Measure from the central subject marker to a point on the camera, or using the focus scale? I am assuming the physical tape measure method, otherwise you have a secondary variable in the mix.

Yes, with a tape measure to the lens board. The focus scale is merely a suggestion. Depending on the subject distance, with a wide open aperture the thickness of the printed line can be the difference.

 

[PeterB]

pbromaghin, have you ruled out the foam as the issue ? Please confirm you have stepped through my (there was a url link here which no longer exists) as I think it presents the potential problems in an order of least to most difficult to repair/rule out.

 

[pbromaghin]

I want to thank everybody for the help. It's a good thing you are doing.

PeterB, I been able to rule some things out, and yes I did give your lessons a good read - outstanding step-by-step instructions. The plane of focus is straight vertical on the angled wall and the equations come out pretty consistently from lens to lens, certainly within the possible error in my measurements. So the lenses are good and the mount, the film plane and ground glass are all square. That pretty much convinces me the ground glass is approximately 1mm closer than the film plane.

I am keeping the thing intact until I get the manual and study the exploded parts diagram, etc. You see, I am a whole lot better at losing parts and breaking things than I am at fixing them I also don't know how different the C33 is from the C330 in your example. There are several other cameras in the stable so I can afford caution and patience.

 

[PeterB]

and I wonder if the C-33 even has the foam. We shall see.

Actually I don't think it does use foam ! The C330 uses threaded posts built into the body to adjust the height of the screen whereas the C33 uses "shim washers on each screw for the focusing screen. If those were missing or put in wrong, you would have the problem you describe. " (see here).

FWIW I found you can purchase a C33 repair manual from here. Double check with them it is for a C33 (as per the image) because it appears incorrectly listed as the C330. It certainly isn't cheap, they list it for £26.95.

EDIT: Just found it cheaper on eBay here. for US$19.20.