Mamiya 645 AM lever

Discussion in 'Medium Format Cameras and Accessories' started by Top-Cat, Aug 4, 2010.

  1. Top-Cat

    Top-Cat Member

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    This might come off as a stupid question, but as I'm skimming through the PRO TL manual, I'm trying to find a certain answer as to the auto/manual lever right next to the lens on a Mamiya 645 PRO TL camera.

    What confuses me is this, is the lens set to automatic exposure when I can see the M and the AE is covered up, or is it the other way around? In a strange way, I just can't see the logic around the construction of the lever and the manual doesn't seem to give any clearly understandable answer to it either.

    Thanks in advance (unless it's an insult to me being a technological egghead).
     
  2. Jon Shiu

    Jon Shiu Subscriber

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    When you can see the M, it's on M. When you can see the A, it's on A.

    Jon
     
  3. MattKing

    MattKing Subscriber

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    The "A" and the "M" may not mean what you think they do.

    The "A" is used for most purposes. It leaves the aperture at it's maximum opening until the instant the shutter is released, at which time the aperture is stopped down to whatever f-stop you have set.

    The "M" is used as a depth of field preview. When M is set (i.e. is visible), the aperture will be at whatever f-stop you have set, so the viewfinder will brighten or go more dim as you adjust the f-stop.

    You need to use the A setting if you are using the in-prism meter.

    You would use the M setting if you had the lens on a bellows, or anything else that does not actuate the aperture at time of exposure.
     
  4. John Koehrer

    John Koehrer Subscriber

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    * What he said. ^
     
  5. 2F/2F

    2F/2F Member

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    The A and the M refer to how the stopping down of the diaphragm is controlled, not to exposure.

    Long, long ago, in the dark ages, automatic aperture, which is the norm today, did not exist. This means that the aperture was directly controlled by the f stop collar on the lens, completely independently of the camera body/shutter. If you set it to wide open, the aperture was wide open. If you set it to f/8, the aperture was at f/8. This means that on an SLR camera, if one wanted to compose and focus wide open, but shoot at another aperture, one had to open up the diaphragm to focus, and close it back down by hand before shooting, and open up again to compose and focus the next shot. This is manual aperture, and the Mamiya allows you to set the diaphragm to work in this way.

    Automatic aperture means that the setting on the f stop collar is not a direct control of the aperture, but is a pre setting. It does not actually affect the size of the aperture until right before the shutter opens. The aperture remains wide open until you fire the shot off. Then, after the shot is taken, the aperture opens back up. A mechanical or electronic linkage between the camera body and the lens tells the aperture when to stop down and reopen. This is the standard way most SLRs have operated since the SLR in general came into prominence, though there are exceptions.

    Pentax cameras have the switches as well.

    So, when you see a manual focus lens that has the word "auto" as part of its name, it is in reference to the way the diaphragm is controlled, not to focus or exposure.