Mamiya TLR - 180 mm lens sharpnes

Discussion in 'Medium Format' started by rick_strome, Jun 14, 1998.

  1. I have an older Mamiya C33 with a 180 mm lens. The last set of pictures I took indicated that the sharpness of the lens was poor.
    I have read that there can be a focus misalignment between the top and bottom lens causing the bottom lens to be slightly out of focus. Thus, when the top (viewing lens)appears properly focused, the bottom is actually out of focus. However I do not know if the above problem exists All I know is that pictures taken are not sharp.
    Does anyone know how you can test for the above problem without being a camera repair technician?
    Thanks, Rick
     
  2. If you check the 'TLRs' section of the recent archive, you'll find several topics on focusing alignment.

    <p>

    'The last set of pictures'? Is this a problem that has just started? The only reasons that a lens pair might be misaligned is shock, or someone fiddling with the lens (such as loosening the retaining ring so that any shims drop out). I'm assuming that it was factory perfect!

    <p>

    Is this the only lens you have, or does it apply to all lenses?

    <p>

    It is just possible to mis-mount a lens so that it isn't fully flat on the lens board, but I doubt the auto-cocking would have worked.

    <p>

    The lens board could be mis-aligned, but that would require a substantial impact. These are tough cameras.

    <p>

    You put 220 film in by mistake? Yes, it's been done - and not just on these cameras.

    <p>

    The focus screen could be mis-aligned, especially if it has been removed recently.

    <p>

    Was the camera back latched fully home on both sides? If not, that can affect the pressure plate alignment.

    <p>

    Summary: Only fiddle with the 180mm as a last resort.
     
  3. If there are problems with the misalignment, than something in front or behind the main subject should be in focus: allways behind or allways to short. However if you discover this, any of the problems Graham wrote about should be considered as well. If it is misalignment, then it could be the camera as well.

    <p>

    So I suggest you shoot some test negs/slides of e.g. graphity on a wall, take notes of where you set the focus and look at the outcome where it is most clear. Perhaps you want to repeat a few times: Defocus, focus, shoot. Use a tripod and have a look whether all are out by a similar amount. Use a wide aperture (4.5 and 5.6) for the test.
     

Share This Page