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  1. #11

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    Quote Originally Posted by Steve Smith View Post
    My pre-AI Nikkors fit on my FG. The ridge does not seem to interfere with the AI tab.

    The aperture stops down when the shutter is fired but how can it meter if it doesn't know how far away from wide open, the aperture is set?
    Steve.
    I always assumed that the sequence of events for all aperture priority capable manual bodies start with the lens being stopped down followed by a last meter reading at actual aperture setting and that is the case with the FG. Like you, I was able to mount a pre AI lens on my FG that doesn't interfere with the tab and in aperture priority mode tested and verified the assumption. Set it wide open and it fires at the metered speed. Turn the aperture to smallest and as expected the meter is the same as indicated wide open as the tab is not moving. Fire the shutter and now the exposure time is much longer as appropriate to the small aperture.

    Of course aperture priority capable manual bodies that meter off the film - like the Olympus OM2, 2S & 4 as well as the Pentax LX, will continue monitoring the scene in real time for light changes and varies exposure time accordingly.

  2. #12

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    Quote Originally Posted by Les Sarile View Post
    I always assumed that the sequence of events for all aperture priority capable manual bodies start with the lens being stopped down followed by a last meter reading at actual aperture setting and that is the case with the FG. Like you, I was able to mount a pre AI lens on my FG that doesn't interfere with the tab and in aperture priority mode tested and verified the assumption. Set it wide open and it fires at the metered speed. Turn the aperture to smallest and as expected the meter is the same as indicated wide open as the tab is not moving. Fire the shutter and now the exposure time is much longer as appropriate to the small aperture.

    Of course aperture priority capable manual bodies that meter off the film - like the Olympus OM2, 2S & 4 as well as the Pentax LX, will continue monitoring the scene in real time for light changes and varies exposure time accordingly.
    This is not the sequence of events for all aperture priority bodies. Imagine the shutter lag this would add to camera that use a mirror relay meter! Also, the whole point of Nikon's AI-S 'upgrade' with respect to aperture linearity would be lost. What you are experiencing is due to the FG having some elements of the FA's 'closed loop' exposure system- if it detects that the lens isn't AI-S, it tries to correct the exposure.

  3. #13
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    I will have to find my FG manual to check, but I think in manual mode, it measures the light at the time of exposure so assuming the aperture has closed down, it should be able to work.

    I don't see how aperture priority can work though.


    Steve.

  4. #14
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    Quote Originally Posted by LiamG View Post
    This is not the sequence of events for all aperture priority bodies. Imagine the shutter lag this would add to camera that use a mirror relay meter! Also, the whole point of Nikon's AI-S 'upgrade' with respect to aperture linearity would be lost. What you are experiencing is due to the FG having some elements of the FA's 'closed loop' exposure system- if it detects that the lens isn't AI-S, it tries to correct the exposure.
    What?
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  5. #15

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    Quote Originally Posted by Steve Smith View Post
    I will have to find my FG manual to check, but I think in manual mode, it measures the light at the time of exposure so assuming the aperture has closed down, it should be able to work.

    I don't see how aperture priority can work though.


    Steve.
    On page 21 of the FG manual Nikon mentions that the camera goes into 'closed loop' mode in P and A; I guess it probably reads the exposure off the film plane after the mirror has gone up, if it waited for the aperture to stop down before it fired the mirror, that would slow down everything- it might, though, I don't own one to check with.

  6. #16
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    Quote Originally Posted by LiamG View Post
    On page 21 of the FG manual Nikon mentions that the camera goes into 'closed loop' mode in P and A; I guess it probably reads the exposure off the film plane after the mirror has gone up, if it waited for the aperture to stop down before it fired the mirror, that would slow down everything- it might, though, I don't own one to check with.
    Then I stand corrected. I knew it did that for P but thinking about it, there's no reason why it can't do it in A too.

    EDIT: I have just tried it and it does appear to work in both A and P.

    In which case, the AI indexing only really helps you in showing the user what the shutter speed will be in A and P modes. It is most useful when manual shutter speeds are being used.


    Steve.
    Last edited by Steve Smith; 05-06-2013 at 01:31 AM. Click to view previous post history.

  7. #17
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    With Ai you don't have to do the nikon shuffle with twisting the aperture ring back and forth, this is the real benefit.Mount the lens and you are done.
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  8. #18

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    Quote Originally Posted by LiamG View Post
    On page 21 of the FG manual Nikon mentions that the camera goes into 'closed loop' mode in P and A; I guess it probably reads the exposure off the film plane after the mirror has gone up, if it waited for the aperture to stop down before it fired the mirror, that would slow down everything- it might, though, I don't own one to check with.
    Too bad you don't own one as it is easy to check. Good point that you brought up reading off the film plane as in fact it has a backward looking sensor that it could possibly meter after the mirror is raised but apparently that is only used by the TTL flash.

    Unfortunately I don't have the magazine review of the FG that may have detailed out the sequence like it did for the OM2 but it is easy enough to test. So I did the exact same test as before except that this time I covered the backward point meter cel in the box. Meter wide open it fires at a fast shutter then stop the lens down - meter is unchanged as the tab is not actuated, but shutter is much slower when fired. Conclusion is therefore that it must takes one last look at the meter prior to raising the mirror.

    BTW, the whole sequence would still take the same time whether if it looks at the meter prior to raising the meter or after by reading off the plane. Since these are no longer CDS cels, metering is fairly instantaneous.

  9. #19

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    I don't think it read the film plane but rather made a stop down reading before the mirror goes up.

  10. #20

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    OK we can officially close out the FG metering sequence - http://imaging.nikon.com/history/cousins/cousins12-e/

    Scroll down to the section "Instant stop-down metering" it lists the sequence of events as stop down, read meter then flip mirror.

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