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    brian steinberger's Avatar
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    Mamiya 6 electronic shutter question

    I've owned and used two Mamiya 6 bodies for years now and there's still one area I'm unsure of.

    I know that the shutter speed is electronically controlled by the camera body but does the body control the amount of time the shutter is open or does the lens? Does the body say 1/60 and execute it, or does the body say to the lens 1/60 and the lens executes it?

    I'm just curious if I should be getting exactly the same exposure with one lens on two different bodies.

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    That's a good question...the battery is in the body so I would assume that the signal originates from the meter when in auto mode but perhaps from the lens when in manual? There is an electrical continuum created between the body and lens when attached though and I certainly don't know enough about it to give you a definitive answer. One thing though, if you are getting divergent exposures from two bodies I would suspect that a battery might need replacing in one of them as the meter could/will give faulty readings if there is a drop in voltage.

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    brian steinberger's Avatar
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    Thanks Matt. I do feel I get slightly less exposure with my one body. Maybe 1/3 stop or so. I mainly use the Mamiya 6 with a spot meter so I'm using the camera in manual, selecting the shutter speeds on the dial. I seem to think the camera controls how long the shutter is open through the contacts on the lens.

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    benjiboy's Avatar
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    Quote Originally Posted by Matt Fattori View Post
    That's a good question...the battery is in the body so I would assume that the signal originates from the meter when in auto mode but perhaps from the lens when in manual? There is an electrical continuum created between the body and lens when attached though and I certainly don't know enough about it to give you a definitive answer. One thing though, if you are getting divergent exposures from two bodies I would suspect that a battery might need replacing in one of them as the meter could/will give faulty readings if there is a drop in voltage.
    I doubt it most camera meters have a wheatstone bridge circuit so if the battery can't make the required voltage the meter drops.dead rather than give progressively worse exposure throughout the battery' s life, I think it more likely that one of the meters.needs recalibrating.
    Last edited by benjiboy; 02-27-2014 at 09:54 PM. Click to view previous post history.
    Ben

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    L Gebhardt's Avatar
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    I don't know whether the camera or the lens times the shutter. My guess is the camera since in the AE exposure mode the speeds are set with much more precision than the full stops that manual offers.

    I think the Mamiya 6 has a similar shutter arrangement to the 7. When I tested the shutter on the Mamiya 7 with the Calumet shutter tester I was shocked to see it was dead on. For example half a second was .500. All the other speeds were right on the money too, out to the last decimal place. I never expected that. My large format lenses have a lot of variation. So if your shutter speeds are variable your equipment probably needs a tune up.

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    brian steinberger's Avatar
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    Quote Originally Posted by benjiboy View Post
    I doubt it most camera meters have a wheatstone bridge circuit so if the battery can't make the required voltage the meter drops.dead rather than give progressively worse exposure throughout the battery' s life, I think it more likely that one of the meters.needs recalibrating.
    I'm curious about setting one camera to say f/8 at 1/60 and same for the other body. The exposures should be identical. Obviously the meters can have variances, but I'm ruling that out since I shoot in manual mode using an external spot meter. So is 1/60 on one camera 1/60 on the other using the same lens? That's what I'm wondering.

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    brian steinberger's Avatar
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    Quote Originally Posted by L Gebhardt View Post
    I don't know whether the camera or the lens times the shutter. My guess is the camera since in the AE exposure mode the speeds are set with much more precision than the full stops that manual offers.
    Is this true?? I've heard this mentioned before but never really knew if in AE mode the camera will shoot in half stops such as 1/45 to 1/90. It's confusing because the VF will always show the full stops and one will be lit up, leading one to believe that the camera only fires in full stops in AE mode and that the particular speed which is lit up is the speed that is firing.

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    Dr Croubie's Avatar
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    From an electronics standpoint, think about how the camera would communicate with the lens. How many contacts are there?

    For a simple binary-coded shutter speed, you'd need 4 contacts for 16 different shutter speeds, plus power, ground, probably one to trigger the shutter itself, plus whatever else, maybe something for aperture value? Are there that many contacts?

    Or, it could use a serial bitstream telling the lens how long to stay open, then telling the lens to open its timer, all in the space between you pressing the button and the shutter going click. The 6 is from the late 80s, same as EOS system and that had serial communication (for lens data and AF) so it's not unheard of. But I don't think this is very likely because there'd be too much shutter lag with the bauds available back then.

    It's more than likely that there's just one signal from the camera being sent to open and close, and the camera takes care of the timing twixt the two.
    This is even more likely if there's a B or T setting, with those the camera *must* tell the lens when to open and shut. And if it does it then, why not just put the timer in the camera and do it all the time?
    I can't prove it because I don't have one in front of me to pull apart, but that's my 2c worth of Occam.


    Of course, if you've got a problem in exposure, you can always grab both bodies, all your lenses, a spot meter and two rolls of Velvia (for the low-latitude, you can tell when it's out by 1/3 of a stop), shoot every combination you can and see exactly which combinations are a problem (ie, if the same lens on both bodies is a problem, or one body with all lenses)
    An awful lot of electrons were terribly inconvenienced in the making of this post.

    f/64 and be there.

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    brian steinberger's Avatar
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    Quote Originally Posted by Dr Croubie View Post
    From an electronics standpoint, think about how the camera would communicate with the lens. How many contacts are there?

    For a simple binary-coded shutter speed, you'd need 4 contacts for 16 different shutter speeds, plus power, ground, probably one to trigger the shutter itself, plus whatever else, maybe something for aperture value? Are there that many contacts?

    Or, it could use a serial bitstream telling the lens how long to stay open, then telling the lens to open its timer, all in the space between you pressing the button and the shutter going click. The 6 is from the late 80s, same as EOS system and that had serial communication (for lens data and AF) so it's not unheard of. But I don't think this is very likely because there'd be too much shutter lag with the bauds available back then.

    It's more than likely that there's just one signal from the camera being sent to open and close, and the camera takes care of the timing twixt the two.
    This is even more likely if there's a B or T setting, with those the camera *must* tell the lens when to open and shut. And if it does it then, why not just put the timer in the camera and do it all the time?
    I can't prove it because I don't have one in front of me to pull apart, but that's my 2c worth of Occam.


    Of course, if you've got a problem in exposure, you can always grab both bodies, all your lenses, a spot meter and two rolls of Velvia (for the low-latitude, you can tell when it's out by 1/3 of a stop), shoot every combination you can and see exactly which combinations are a problem (ie, if the same lens on both bodies is a problem, or one body with all lenses)
    Thanks for this great response. And a good idea to shoot chromes. I only shoot negative film and believe I'm seeing a small amount of exposure difference between the two bodies. Now I did just have both bodies CLA'd so i'm hoping to run tests tomorrow to see if the "problem" still exists. Unfortunately I do not have any slide film on hand so will have to settle for B&W.

  10. #10
    pasiasty's Avatar
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    Quote Originally Posted by Dr Croubie View Post
    For a simple binary-coded shutter speed, you'd need 4 contacts for 16 different shutter speeds, plus power, ground, probably one to trigger the shutter itself, plus whatever else, maybe something for aperture value? Are there that many contacts?
    You silently assume the communication is digital... and it need not necessarily be so. A couple of years older Bronica SQ uses analogue signalling, you just switch resistors while setting aperture.
    || Cezary Żemis <cezary.zemis@pronet.pl> | www.cezaryzemis.name
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