Where is the metering chip/sensor?

[prodigy2k7]

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?

 

[dEARlEADER]

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....

 

[prodigy2k7]

And why does the mirror in my XTi look semi transparent?

 

[Helen B]

And why does the mirror in my XTi look semi transparent?

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

 

[Bifurcator]

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.

 

[Helen B]

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

 

[Bifurcator]

Here's a picture of the "RGB 1005 segment metering sensor" in the D700:

Image courtesy of Digital Photography Review ( www.dpreview.com )




Image courtesy of Digital Photography Review ( www.dpreview.com )​

And you can kind of see it here in the lower portion of the mirrorbox compartment.



.

 

[Bifurcator]

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

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.

 

[prodigy2k7]

Awesome, thanks! I always feel honored when Helen responds to my msgs

 

[dEARlEADER]

Awesome, thanks! I always feel honored when Helen responds to my msgs

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

 

[Garbz]

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.

 

[prodigy2k7]

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.

Awesome! thanks

 

[Bifurcator]

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.

WHAT??? You mean we can't just open the back, and with the shutter on B depress the shutter release to get a first hand look at the light sensors??



This is a joke pertaining to film cameras and film photographers. :lmao:


.