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02-25-2008, 02:33 PM   #1
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k10d and smc-m mettering

hello, gentle pentaxians . i need some help from you lba infected people.

to be honest from the start, it is a gx10, but i guess that shouldn't make much difference

i finally got the lens i have been dreaming of for a decade or so, since i shoot slrs: 80mm/1.8, well, actually better, i got the smc-m 50mm/1.4, which is 75mm/1.4 on the aps-c, so the same fov, and a maximum aperture i wasn't even dreaming of back then. needless to say i am in love. however there seems to be an issue: metering seems to be quite erratic: every now and then i get completely off-the mark readings, usually overexposing, but not only (using the green button for stop down metering). it seems to happen both with center weighted and spot metering, btw, and when it happens, it does it even if i try it repeatedly (so it's not a glitch, like the aperture not closing fully -- though that should give underexposure). underexposure happens also, but not as often (need to do more tests, though). mettering with the two da "kit" lenses has always been spot on (or as close to always as one would expect), same goes for an old "A" zoom ("exakta varioplan 35-70").

anybody experienced this? may it be i'm overlooking something obvious?

thank you all in advance.

02-25-2008, 02:34 PM   #2
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what mode are you in?

are you using the green button correctly?

remember you have to shoot what you meter...
02-25-2008, 03:32 PM   #3
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manual mode (i was about to not buy the lens, because i had forgotten about that, fortunately i checked the lens itself, the aperture would work fine, so i said "what the hell, i won't let a 50/1.4 pass, i'll gamble". glad i did, i guess i am LBA-inffected, and it just goes to show.. uhm.. "lba is good!" ). as far as i could tell, no way to have it to work in any other mode (?), i guess it's normal, as it needs to stop down, so cannot meter continously, only "on request"

shooting what i metter: ofcourse.

what do you mean by using the green button correctly? i guess i should read up on this little green thing. i hear it mentioned quite often, seems like somewhat of a celebrity in pentax circles
02-25-2008, 04:14 PM   #4
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In M mode the "Green Button" will give you the exposure settings for the current program. So on an non-A lens (M or M42) you have to focus with the aperture wide open and then step down the to the desired aperture to meter. Press the Green Button and the camera will pick the shutter speed for the aperture you set on the lens (assuming that's how you have it set in the custom menu). From there you can of course adjust the exposure settings to your liking. With A lens you don't have to worry about this if the aperture dial on the lens is set to "A" and it will behave just like a newer lens.

02-25-2008, 04:19 PM   #5
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QuoteOriginally posted by tybeck Quote
In M mode the "Green Button" will give you the exposure settings for the current program. So on an non-A lens (M or M42) you have to focus with the aperture wide open and then step down the to the desired aperture to meter. Press the Green Button and the camera will pick the shutter speed for the aperture you set on the lens (assuming that's how you have it set in the custom menu). From there you can of course adjust the exposure settings to your liking. With A lens you don't have to worry about this if the aperture dial on the lens is set to "A" and it will behave just like a newer lens.
I have found, with my K10D and M lenses that the most accurate metering is with the use of the DOF preview to set the exposure. Using the DOF causes the camera to actually stop down the lens to the actual set aperture, then meter. The camera does not know the maximum aperture of the M or K lens, and there can be some exposure inaccuracies.
02-25-2008, 04:49 PM   #6
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There are some threads on the problem if you do a search, most find the k10d will overexpose when at apertures smaller than f4 with manual lens (km). Mine was about 1.5 f stops over at f 8. I put in a *ist D focus screen and it works for me. DOF and green button were both off on mine.
02-25-2008, 06:17 PM   #7
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I have done a lot of testing and can advise the following.

The K10 D has an apparent issue with metering of non AE lenses. At F1.4 it will under-expose by 1 stop, but f5.6 it is over exposing by 1-1.5 stops, peaking at +2 stops by F11 and returning back to 1.5 stops at F22/32.

It seems to be related to the K10D only, my *istD is perfect.
02-26-2008, 12:36 PM   #8
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I'm finding that using M mode holding down the optical preview switch and adjusting the exposure time while watching the meter in the view finder works best.

02-26-2008, 02:26 PM   #9
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hmmm. the plot thickens. i kind of hoped i was just doing something really stupid, and it was just my mistake.

after reading your feedback, it seems like there is indeed some bug with the k10d (firmware? meter electronics? optics on the metering cell behaving weird when the lens is stopped down?)

i am a bit confused.. they don't tell you this, and about the crippled kaf2 mount, when they say "compatible with every lens ever built". hmmm
02-26-2008, 02:56 PM   #10
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I really wish you could just tell the camera what fstop you are using rather than have it say f-- and shrug its shoulders about that.
02-26-2008, 04:36 PM   #11
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QuoteOriginally posted by nanok Quote
hmmm. the plot thickens. i kind of hoped i was just doing something really stupid, and it was just my mistake.

after reading your feedback, it seems like there is indeed some bug with the k10d (firmware? meter electronics? optics on the metering cell behaving weird when the lens is stopped down?)

i am a bit confused.. they don't tell you this, and about the crippled kaf2 mount, when they say "compatible with every lens ever built". hmmm
I believe the "bug" is with respect to the hardware, not firmware.

I have not tried other metering options, only spot metering (which I am highly dependant on for wildlife shots)

I have also tested AE lenses taken out of AE mode, and they behave the same. Furthermore, this problem does not hamper my *istD, which meters perfectly with NON AE lenses, and this remains one reasone I have kept the *istD. It has eveolved into my manual lens body.

It would be very interesting if users of the other bodies *istDS, DL K100, K110 specifically could take a set of shots in manual mode at each detent for apature, metering as the camera suggests, with different lenses, so we could see the performance of other bodies. The best subject is a concrete block wall evenly lit with sunlight. I use the central 1/9 of the frame to evaluate grey scale.
02-27-2008, 12:05 AM   #12
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this is very intriguing. somebody else also mentioned they replaced the focusing screen with one from and ist series, and now it works. unfortunately, i sold the k100d (i will probably get another one some day, i loved it, but needed the money, and wanted the k10d too badly ) , but i will test more with the gx10 and try to figure out a pattern, based on your hints here.

the thing that is most intriguing to me is why the hardware would behave different with different lenses? stop down metering is not the most elegant solution, but it is always the most reliable! (the light is metered directly, if the aperture should not clos correctly, open aperture metering will fail, by making an incorrect assumption).

i will be back with my findings, as soon as i can shoot, if somebody can do it for a k100d it would be great
02-27-2008, 12:34 AM   #13
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QuoteOriginally posted by nanok Quote
i am a bit confused.. they don't tell you this, and about the crippled kaf2 mount, when they say "compatible with every lens ever built". hmmm
Do they really say that? If you read the specification for the camera on the box it came in it says KAF2, KAF and KA lenses, if I'm not mistaken.
02-27-2008, 12:50 AM   #14
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There are two facts:
  1. There is a problem with metering stopped down. This also continues with the K20D. I have tested this.
  2. If you replace the standard L80 screen with a L60 screen (from the istD series) the exposure is just fine. I have tested this. Several others confirmed that, too.
So, what does this mean?
I am not sure, but it appears that they have changed the screen, but forgot to calibrate the meter accordingly.
02-27-2008, 07:50 AM   #15
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QuoteOriginally posted by nanok Quote

the thing that is most intriguing to me is why the hardware would behave different with different lenses? stop down metering is not the most elegant solution, but it is always the most reliable! (the light is metered directly, if the aperture should not clos correctly, open aperture metering will fail, by making an incorrect assumption).
I am not sure what the problem is with the K10 metering, I have heard all sorts of stories, from it was due to the lens coating and specific light colors, to the reflection off the focusing screen (where metering takes it all) as a function of apature and the resulting angles. I don't really know what to believe, and all I can advise it what I have seen, how I tested it, which I have posted many times, and the results. The issue is that the performance seems to be much more related to the apature when stopped down, then specific lenses

I have basically mapped out the exposure accuracy of both DSLRs that I own (*istD and K10D) principally so I can be more assured of the pictures I get back.

I want to see what the different focusing screens do, but it is an expensive proposition, which is why I keep promiting that users with different lenses and camera bodies (plus focusing screens) test and post the data, at least that way we can make a decision before buying the screens etc.

Perhaps this is another area for Adam and the forum. A camera body database, with reviews and performance information from user's tests.
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