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10-02-2009, 08:34 AM   #1
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k20d metering with M lens

Looks like this issue has been beaten to death already. I was trying out my newly acquired M-200mm f4 lens and, like everyone else, I'm seeing over-exposure all over the place with stop down metering (green button). Same with Av mode where I adjusted EV-comp as I stopped down the lens. The shutter-speed shown in M after hitting the green button also doesn't match that of Av mode -- off by a at least a factor of 2 or 3 -- yet they both produce the identically exposed picture, as confirmed by the histogram.

I'm getting better, predictable result by starting off wide open in Av and get a shuttter-speed reading, then switching to M and set that shutter speed. I adjust shutter-speed from there as I close down the aperture. I was hoping to just stay in AV and adjust EV instead, but that didn't work out well, though it seems more accurate that green-button method.

May be I need to re-hash the sunny-16 table again.

PS. Observations based only on the SMC M 200 F4. I kept a constant ISO.

10-02-2009, 10:05 AM   #2
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you're quite right, this has been beaten to death in the forums

I do have a couple of questions however.

you say that you meter in AV mode, and get differences when stopped down between AV and manual?

are you aware that in AV mode the camera does not stop the lens down or take aperture into account at all, but shoots wide open? I know this is a fundamental question but I have to ask.

Also, in manual mode, when presing the green button, at different apertures, can you describe the error in exposure more accurately.

Specifically, I would expect that wide open this lens should meter sopt on, (i.e. if you shoot at a uniformly lit surface, it has a histogram value of about 120. By between F8 and F11 this rises to about 180-200 histogram, and then by F32 drops back to about 160

Is that right? Only asking because that is about how my K10D works.

If this is the case, you could set the exposure compensation (I think it works in manual on the K20 it does not on K10) to under expose by about .7 ev and your exposure should then be always between -.7 ev and about +.7.

You will find the worst prroblem is actually when you have fast lenses as they will underexpose by 1 ev wide open,
10-02-2009, 11:38 AM   #3
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QuoteOriginally posted by Lowell Goudge Quote
you say that you meter in AV mode, and get differences when stopped down between AV and manual?

are you aware that in AV mode the camera does not stop the lens down or take aperture into account at all, but shoots wide open? I know this is a fundamental question but I have to ask.

Also, in manual mode, when presing the green button, at different apertures, can you describe the error in exposure more accurately.
Yes, I found out, thru some previous posts, that in AV mode the camera doesn't take the aperture ring setting into account. It does meter a reading for wide-open aperture. What I tried doing is start off metering wide open in AV and apply EV comp as I close the shutter -- +1EV when going from f4 to f5.6, +2EV to f8 etc.

In M mode with green button, there is a slight underexposure at f4, may be 0.3EV or so. It starts to overexpose from f5.6, getting worse as I stopped further down -- by more than 1.5EV relative to f4. I didn't go above f11, as the shutter speed was getting to low for my liking.

I'm not exactly getting different results between M-with-green-button and AV-with-EV-COMP -- the histograms are identical, i.e., exposure identically off. But I'm not sure that the shutter-speed shown/recorded when pressing the green button is the actual, fired shutter speed, which appears to be faster.

I'll have to do a more careful test, may be this weekend if the sun ever comes out.
I should try the DOF lever method in M mode too. I need to re-assign shutter-speed selector from front to back wheel for that.
10-04-2009, 06:40 AM   #4
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It's a mixed bag of nuts...

the behavior is really so dependent on the metering mode (I find that spot works best most of the time - segmented almost never works for me) and your subject.

For example, with a typical landscape, spot metering & M mode, the green button exposure is typically within a stop in my experience. Since that landscape is not moving, I don't mind, and have all the time I need to make an adjustment

When I'm shooting macros of glass art (dark, rich colours), I automatically adjust by three stops because I am not metering a mid-tone, and again I'm usually within a stop of where I want to be.

10-06-2009, 08:50 AM   #5
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QuoteOriginally posted by singlespeed Quote
the behavior is really so dependent on the metering mode (I find that spot works best most of the time - segmented almost never works for me) and your subject.

For example, with a typical landscape, spot metering & M mode, the green button exposure is typically within a stop in my experience. Since that landscape is not moving, I don't mind, and have all the time I need to make an adjustment

When I'm shooting macros of glass art (dark, rich colours), I automatically adjust by three stops because I am not metering a mid-tone, and again I'm usually within a stop of where I want to be.
I was under the impression that in manual mode, with M or K lenses, the camera always defaulted to center_weighter metering, which is what I had the dial set to.
10-06-2009, 10:15 AM   #6
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QuoteOriginally posted by wasim_altaf Quote
I was under the impression that in manual mode, with M or K lenses, the camera always defaulted to center_weighter metering, which is what I had the dial set to.
matrix defaults to center weighted, because matrix metering needs to know the aperture data that is on the A lenses.

Spot metering always works with any lens
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