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02-22-2009, 05:37 AM   #1
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Km no matrix metering with pentax M lense?

Hi everyone,

I was trying an old M lense on the K-m and figured it didnt let me use matrix metering, only spot and center weighted

i dont have my K20D with me at the moment, but i think with the k20d i can still use matrix metering mode. or can it not? (since it is mechanical button setting and not software, perphas it is set to matrix but uses center weighted?)

and why would it not be possible to do so?

if you have any ideas

regards

P

02-22-2009, 05:45 AM   #2
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the K20D canīt do matrix either. It used to be the same thing with film bodies and M-lenses too. Not shure why this is the case...
02-22-2009, 06:07 AM   #3
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Just to add that the K100D can't do it either.
02-22-2009, 06:17 AM   #4
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NO Pentax camera can do Matrix metering with M lenses.

02-22-2009, 06:45 AM   #5
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QuoteOriginally posted by ftpaddict Quote
NO Pentax camera can do Matrix metering with M lenses.
Just because matrix metering uses distance information, focal length and maximum aperture of the lens which no M lens can tell. Although A lenses don't tell the former two neither, they at least can tell the maximum aperture, but then the matrix metering will not be as accurate as it should be, with A lenses.
02-22-2009, 06:47 AM   #6
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QuoteOriginally posted by debbie Quote
the K20D canīt do matrix either. It used to be the same thing with film bodies and M-lenses too. Not shure why this is the case...
K and M Lenses lack the needed contacts of the A and newer lenses that transmit the min and max aperture. These contacts are needed in order to do matrix metering. I think there was a lens modification that would trick the camera into using matrix metering but it required drilling out holes in the lens mount and filling them with an apoxy of some sort.
02-22-2009, 07:22 AM   #7
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QuoteOriginally posted by RiceHigh Quote
Just because matrix metering uses distance information, focal length and maximum aperture of the lens which no M lens can tell. Although A lenses don't tell the former two neither, they at least can tell the maximum aperture, but then the matrix metering will not be as accurate as it should be, with A lenses.
interesting,
do you have any idea why matrix metering needs all these bits of information?
i'm just curious at understanding how it works,
i have found kenrockwell has some explanation on how matrix metering works

my ignorance thought it only measured how much light the sensor received on different segment, and evaluated a mean of something
seems it is actually much more complex. now i understand why i have such a hard time exposing my pictures using old m42 and M lenses.

thanks
02-22-2009, 07:06 PM   #8
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Evaluative/Matrix Metering

Evaluative Metering, by its name, is just a knowledge based artificial intelligent system to analyse the whole scene with different lighting distribution and pattern which tries to find out an "optimal" and "balanced" exposure value from time to time.

As such, it would try to find out or simply guess the area and subject(s) of interest in the frame.

With more additional technical data fed into the system as inputs, it could guess the scene and find out the subjects of interest more accurately, with a higher hit rate. Ditto for the number of metering segments, the more segments the evaluative metering system has, the more data it could gather and analyse.

In this case, the subject distance (measured by the AF system), the focal length chosen or at least the maximum aperture of the lens (for the light/energy received by different metering segment), are just the crucial basic information which the evaluative meter needs to know before it could do its job.

Old Pentax pre-A K-mount lenses don't tell the maximum aperture, they only told the differences in f-stop between the maximum aperture and the aperture which is to take the picture. For more information about the technical evolution of the Pentax K-mount, here is my very old article posted at my website:-

K Mount Metering & Exposure Bases - A Technical Brief

QuoteOriginally posted by phler2 Quote
interesting,
do you have any idea why matrix metering needs all these bits of information?
i'm just curious at understanding how it works,
i have found kenrockwell has some explanation on how matrix metering works

my ignorance thought it only measured how much light the sensor received on different segment, and evaluated a mean of something
seems it is actually much more complex. now i understand why i have such a hard time exposing my pictures using old m42 and M lenses.

thanks


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