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  1. #41
    PeterB's Avatar
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    Quote Originally Posted by Marc B. View Post
    I think the OP needs a different focusing screen, or needs to shim the focusing screen. Firstly, you're not attacking the problem by addressing/eliminating the simplest, or most common area that causes focusing problems, and that is usually the focusing screen.
    Hi Marc, assuming your reply was directed to me, here are my thoughts.


    The Mamiya C330f service manual contains only two sections pertaining to adjusting the focus.
    1. The first section seeks to ensure the front of the camera is parallel to the film plane.
    2. The second section ensures the distances travelled by the light rays (from taking lens to film and from viewing lens to view screen) are the same. It works off your assumption but instead of using shims for the focussing screen (as was the case with earlier models) it gets one to adjust the height of the screen by screwing up or down three posts in the camera.
    Now I have proven that my camera has problem number 1. See photos of the dial gauge I posted yesterday in this thread for evidence. Why would I now try and solve that parallelism problem by moving the viewing screen up and down when the makers of the camera instruct us to solve it a different way ? (this way detailed here from my post #35 in this thread)

  2. #42
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    I'd say you're on the right track with where you're going. Any idea why the front "standard" is out of parallel? I have two c330s and never seen a consistent focus problem with either.

    Perhaps a rack issue?
    Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.

    http://www.flickr.com/kediwah

  3. #43
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    Hi clayne. I'm not sure why the front is not parallel to the film plane. I bought it from the original owner a few years ago, I could always ask if they dropped it. At least the service manual tells me how to adjust i, but I am having a real problem getting those last 3 screws out to do the adjustment !

  4. #44
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    Do they sell micro-sized impact screwdrivers? That's basically what you need - it's a big piece of metal + screwdriver bit that when you hit it with a hammer, it turns in a given direction and also pushes into the head of the screw. However, without going that far, I think the screws might be a bear because they were applied with thread-lock, most likely to combat vibration, etc. Check out something like this: http://www.radiocontrolzone.com/showthread.php?t=20290 and possibly search around more on how to loosen the thread-lock.
    Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.

    http://www.flickr.com/kediwah

  5. #45
    PeterB's Avatar
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    Thanks Clayne. I have recently also read that heating the screw will melt and then loosen the threadlock. You've made me realise that penetrating oil is not going to work now ! I will get apply the tip of my soldering iron to the screw and hope that will do the trick. There isn't much nylon in the immediate area.

  6. #46
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    Also, don't forget the trick with a screwdriver and a pair of vice-grips. If you can apply sufficient downward pressure to the head such that the screwdriver won't slip or otherwise strip the head, you can use vice-grips attached to the screwdriver body and counter-clockwise rotation to make use of the high mechanical advantage.
    Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.

    http://www.flickr.com/kediwah

  7. #47
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    Quote Originally Posted by clayne View Post
    Also, don't forget the trick with a screwdriver and a pair of vice-grips. If you can apply sufficient downward pressure to the head such that the screwdriver won't slip or otherwise strip the head, you can use vice-grips attached to the screwdriver body and counter-clockwise rotation to make use of the high mechanical advantage.
    Tried that last night !! No success unfortunately. I bought some locking pliers just for that (since I didn't own any). I am getting close to deforming the phillips screw head right now, so I'm going to try the heating option as I'd rather not drill it out and tap a larger thread !

  8. #48
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    Ah yeah, you definitely don't want to damage the screw head. Although, do be aware that if it comes to that you can drill just under the dimensions of the thread size and "crumble" the screw out without having to tap to a large size. But I'd imagine you would want to seriously avoid that solution in all cases...

    I bet it's the thread lock.
    Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.

    http://www.flickr.com/kediwah

  9. #49
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    Another update. After 2 nights of struggles and more discoveries I've now come full circle.

    In summary, the apex of each lens was always at the same distance from the film plane, so I will now proceed with adjusting the height of the viewing screen as per the repair manual. Hopefully this will solve the discrepancy of 0.6mm lineal adjustment in focus required when focusing using the viewing screen or a ground glass on the lens plane.

    Details: I was unable to unscrew any of the 3 screws needed to make the front of the camera parallel with the film plane. I tried heating them with a soldering iron, then found the camera body is a superb metal heatsink so I moved on to a butane torch ! That didn't melt the threadlock so I opted for freezing spray to try and shrink the screw faster than the hole hoping it would crack the threadlock but to no avail !!

    So then I decided to change tact. Rather than just measuring to the front of the camera body, I decided to measure to the apex of each front lens element (see attached pics.).

    Click image for larger version. 

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    It then occurred to me that perhaps one of my lens shims was so thick because it was put in there to compensate for the camera front not being parallel.
    To prove this I discarded my wooden slab and had a piece of plexiglass/perspex cut to support the camera on its film plane in a very steady fashion. Its dimensions were WxLxH=63x120x20mm
    See pic.

    Click image for larger version. 

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    This gave me better repeatability in the measurements. I also bought a flat piece of thick off-cut perspex to rest everything on.

    I then realised that by putting each shim back in place (a thick one for the viewing lens and a thin one for the taking lens) that when I measured to the apex of each lens' front element, they were nearly identical distances away from the film plane. In fact there was only a 0.03mm (=0.0012") difference !! Their apexes were aligned all along despite there being a 0.6mm fall across the entire camera front under the lens plate. As to whether using lens shims to solve this problem is an acceptable solution or not, I'm not sure. I say this because the lenses are still not perpendicular with the film plane (as the lens plate is parallel to the camera front but not parallel to the film plane). The lenses are just offset with shims so that their apexes are the same distance from the film plane. The lens axes are about 0.35 degrees tilted away from being perpendicular. I don't know how this affects critical focusing at any distances @f2.8. I suppose I could think about it some more and do the maths, but not right now.

    I think what has happened is that in either a prior repair job or even when it was made in the factory, somebody decided to fix the anti-parallelism in this less than optimal manner.

    Short of drilling out those screws I mentioned above the only other way I can think of to make the lens axes perpendicular with the film plane is to place a small shim between the front of the camera body and the lens plate at one end and re-shim the lenses.

    Anyway, my next task is to adjust the viewing screen height to compensate for the 0.6mm lineal difference btwn it's light path and the film plane's light path.

  10. #50
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    Yeah ! After much thought and adjustments I finally have everything parallel and perpendicular to within +/- 0.07mm and 0.05deg across the entire range of focus. (it was originally out by 0.6mm and o.35deg). I calculated that the depth of focus@f2.8 focused at infinity with the 80mm lens is about 0.25mm so this is well within acceptable limits.

    Just to remind you, the problem I was trying to solve was that the front plane of the camera's body (with lenses removed) was not parallel to the film plane. The bottom was 0.6mm further out than the top. I think it was either dropped by its former owner or even assembled by a dodgy assembly line worker at Mamiya.

    I decided to solve this problem by shimming the underside of the lens plate forward by 0.6mm and removing the thick 0.4mm shim on the viewing lens. This made the lens axes perpendicular with the film plane. The next step I took was to raise the 3 posts below the focussing screen by about 0.6mm (about 1.5 turns each). Now the image in the viewfinder focuses at the same point an image on the film plane does. At the film plane I placed 3mm perspex/plexiglass with scotch magic tape on the side facing the lens for a poor man's ground glass. I tested the focus tonight at about 4 different distances from 50cm to 20m.

    Soon I'll run a test roll through of a tape measure and some fence pickets to be 100% certain !


    I

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