Where is the metering chip/sensor?

Discussion in 'Photographic Discussions' started by prodigy2k7, Aug 1, 2008.

  1. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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    So, where does the metering take place in a camera? Not in the lens since its all glass visibly, you can see right through it. Not behind the mirror since the shutter is closed. So that also cancels out the sensor. Is it somewhere infront/behind the pentaprism? Infront of viewfinder etc... Or is it somewhere near the autofocus motor and autofocus points?
     
  2. dEARlEADER

    dEARlEADER TPF Noob!

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    thats a good question..... i'd like to know that too....

    i know the metering is mostly ttl so somehow it's getting through the lens....
     
  3. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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    And why does the mirror in my XTi look semi transparent?
     
  4. Helen B

    Helen B TPF Noob!

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    Because the metering cell and the autofocus sensors are behind it?

    Some SLRs meter off the ground glass screen and some meter off what comes though the semi-silvered mirror. There may be a secondary mirror behind the main mirror.

    Best,
    Helen
     
  5. Bifurcator

    Bifurcator TPF Noob!

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    Some meter off the film too or off the sensor which I think is superior. This is Olympus's trick. It means that if the light levels change during exposure and you're in an automatic mode that the camera will respond dynamically and increase or decrease the aperture and/or shutter.

    The sensors themselves are usually located in the mirror-box and there's commonly between one and five of them in there for metering different parts of the frame etc.
     
    Last edited: Aug 1, 2008
  6. Helen B

    Helen B TPF Noob!

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    Good point. There are also a few Minoltas that meter off the film during exposure when in auto and at shutter speeds slower than sync speed. I used to have a Minolta that did that, but I hardly ever use auto exposure so it was unimportant to me. It's very good for TTL flash control, however. Many cameras have that, even a few that don't have true TTL metering at other times.

    It must be quite hard to meter off a sensor during exposure because the surface isn't as diffuse as the surface of film.

    Best,
    Helen
     
    Last edited: Aug 1, 2008
  7. Bifurcator

    Bifurcator TPF Noob!

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    Last edited: Aug 1, 2008
  8. Bifurcator

    Bifurcator TPF Noob!

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    Yup. I forgot to mention it's use in flash control. Thanks!

    On metering off the sensor that's a good point. I can't remember where I read that. If I find it again I'll come back with the link. I was kinda of surprised when I read it though because isn't a CCD/CMOS/NMOS already sort of a light sensor in a way? I would have thought that they would figure a way to use some sample points and average during exposure for that kinda thing. Or maybe that's what they were doing? It didn't show a picture or anything and you know reviews these days. :D
     
  9. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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    Awesome, thanks! I always feel honored when Helen responds to my msgs :)
     
  10. dEARlEADER

    dEARlEADER TPF Noob!

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    geesh... bifurcator took the time to post those images and still gets no respect....
     
  11. Garbz

    Garbz No longer a newbie, moving up!

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    Tough love on this forum. But he is right. AF and metering are done in the bottom of camera off the semi transparent mirror. If you pull of your lens and move the mirror up, or put it in cleaning mode you can see parts of the AF unit in the base.
     
  12. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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    Awesome! thanks :)
     

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