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03-06-2008, 04:56 PM   #1
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Exposure metering with K10D

It seems to be commonly accepted that the K10D tends to underexpose right? If I set EV comp to about +0.7 I seem to get a decent exposure under "normal" lighting conditions. Does that seem about right for most of you? So, if I have a backlit situation I'll have to go to probably +1.7 (depending on the backlighting) to get a good exposure. And, since overexposing "a little" (how much is a little?) is known to help reduce noise in high ISO shots I suppose I should start off with, what, maybe + 1.0 or +1.3 ?

Also, why didn't Pentax figure out what everyone seems to know and tweak the metering system so that it exposes properly at EV comp 0.0? Forgot to say I'm using the Tamron 18-250 and use center weighted metering (seems to be a little more accurate than matrix).

03-06-2008, 05:46 PM   #2
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QuoteOriginally posted by Workingdog Quote
It seems to be commonly accepted that the K10D tends to underexpose right?
Technically it meters just fine..... What one "likes" and what is "correct" are sometimes 2 different things.
Good reference re: lightmeter calibration:
http://doug.kerr.home.att.net/pumpkin/Exposure_Calibration.pdf
........That’s not surprising. Had they adopted a substantially
non-standard metering calibration, then a photographer who preferred
to use a free-standing exposure meter would get a significantly
different exposure indication for a certain scene than the camera’s
own metering system would give—a likely cause of consternation.
So that leaves Canon with only the possibility of achieving their target
value of Hu/Hsat by using a non-standard rating of ISO sensitivity—a
rating that is about 0.74 that which would be determined under ISO
12232. In other words, the sensitivity that is designated “ISO 100” by
Canon would probably be rated at about ISO 135 under ISO 12232.

In other words the higher exposed images of the Canon DSLR's (which unfortunately are the basis for many to judge other cameras) are created by underrating the iso sensitivity of their sensors... Over a long period of time I rarely heard Nikon shooters complain that Pentax "underexposes".

QuoteOriginally posted by Workingdog Quote
If I set EV comp to about +0.7 I seem to get a decent exposure under "normal" lighting conditions. Does that seem about right for most of you? So, if I have a backlit situation I'll have to go to probably +1.7 (depending on the backlighting) to get a good exposure. And, since overexposing "a little" (how much is a little?) is known to help reduce noise in high ISO shots I suppose I should start off with, what, maybe + 1.0 or +1.3 ?
Depends on the scene and what you want to do, really...
Short discussion but almost all the details are correct: ND filters, multiple exposures and HSS flash (which is optional depending on the iso and intensity of the backlight) are really the only option short of deciding what to throw out.
Exposure/DR question: spot-metering help: Pentax SLR Talk Forum: Digital Photography Review

QuoteOriginally posted by Workingdog Quote
Also, why didn't Pentax figure out what everyone seems to know and tweak the metering system so that it exposes properly at EV comp 0.0? Forgot to say I'm using the Tamron 18-250 and use center weighted metering (seems to be a little more accurate than matrix).
Because it does as it was designed based on the ANSI standards for meters and iso....
Canon had to fudge the iso by about 1/2 stop in order to look "right". Nikon's meters vary by target audience and some will complain both ways depending on what model..
Matrix metering is a "crapshoot" since the camera is deciding on what's important and whats not. Nikon uses like a 10000 scene "look up table" to decide how to meter. Doubt if Pentax is even that sophisticated.
In case your under the impression that Pentax is the only camera criticized for metering, here is just one of 1000's of examples:
Re: Metering on D80 vs. D70?: Nikon D80/D70/D50/D40 Forum: Digital Photography Review
All stemming from the same "urban legend"
Meters Don't See 18% Gray by Thom Hogan
Histograms by Thom Hogan
Read Thom Hogan's analysis...: Nikon D80/D70/D50/D40 Forum: Digital Photography Review

Last edited by jeffkrol; 03-06-2008 at 08:21 PM.
03-06-2008, 05:50 PM   #3
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Use your histogram. Get it as far to the right with out touching the right side. This will keep noise to a min. I find myself shooting +.3 or +.7. Unless I have an m42 lens on then I usually end up in the +1.0 +1.7 range. I believe they wanted to try to avoid blowing out highlights thats why they tend to meter on the negative side. Thats just my opinion no fact behind it.
03-06-2008, 08:33 PM   #4
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QuoteOriginally posted by Workingdog Quote
It seems to be commonly accepted that the K10D tends to underexpose right? .
I have read this type of post a couple of times, but it has not been my experience with the k10d that it "tends to underexpose." I also disagree that this is commonly accepted.

I think jeffkrol did a very nice analysis here in his post above. I want to add that do people really think that Pentax engineers are clueless about designing the metering system? If there really was a fundamental underexposure problem in the entire k10d line, do you think that they would be blind to it, and us amateurs and semi-pro's have some insight that they don't?

I propose that there are two alternative and simpler explanations for these "underexposure problems":
1) a manufacturing defect in a particular camera such as a calibration error in a light sensor.
2) Users being unfamiliar with the way the metering system based on reflected light works, and how to use it effectively.

If pressed, I would have to say that #2 is the explanation in most cases.


Last edited by PentaxPoke; 03-06-2008 at 08:47 PM.
03-07-2008, 06:46 AM   #5
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If I shoot 40 different photos under different situations with ev comp set at 0 and 30 of them are underexposed I don't believe its a matter of being unfamiliar with the way a metering system works.Why would you not have the camera expose to get 30 of the 40 pictures correctly exposed and have maybe 10 overexposed? Even if I use center weighted metering I have to use + exposure compensation....Bob
03-07-2008, 06:57 AM   #6
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from my humble experience, if you take a photo of an evenly immuminated uniform colored wall, with your camera (regardless of metering mode) you shoud get a photo with a histogram value of about 125. i.e. that the exposure is right in the middle.

If this is what you get, the metering is working corerectly.

then, (and this is now a question of your other settings, specifically contrast and bright vs normal mode) every 40-50 points of grey scale represents 1 f stop.

When you get below 25 or above 230 things become non linear, but between 25 and 230 greyu scale you have 6 stops of exposure lattitude in minimum contrast and 4 stops in maximum contrast modes. and 5 stops in RAW because contrast only impacts JPEG
03-07-2008, 07:39 AM   #7
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QuoteOriginally posted by Lowell Goudge Quote
from my humble experience, if you take a photo of an evenly immuminated uniform colored wall, with your camera (regardless of metering mode) you shoud get a photo with a histogram value of about 125. i.e. that the exposure is right in the middle.

If this is what you get, the metering is working corerectly.

then, (and this is now a question of your other settings, specifically contrast and bright vs normal mode) every 40-50 points of grey scale represents 1 f stop.

When you get below 25 or above 230 things become non linear, but between 25 and 230 greyu scale you have 6 stops of exposure lattitude in minimum contrast and 4 stops in maximum contrast modes. and 5 stops in RAW because contrast only impacts JPEG
not that is incorrect. ANSI standards would put it at closer to 110......
Thanks to Mr. Hogan, this is what you should get (and he is not the only one BTW:
If you own a Canon yes.. see my post above and Mr. Kerr's papers.
Histograms by Thom Hogan
03-07-2008, 07:44 AM   #8
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QuoteOriginally posted by jeffkrol Quote
not that is incorrect. ANSI standards would put it at closer to 110......
Thanks to Mr. Hogan, this is what you should get (and he is not the only one BTW:
If you own a Canon yes.. see my post above and Mr. Kerr's papers.
Histograms by Thom Hogan
I can live with that, I am going by tests I have done, and the problem is that the difference is within 1/3 stop therefore it may be a question of being below the threshold of changing to the next 1/3 stop.

03-07-2008, 07:53 AM   #9
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QuoteOriginally posted by robert Quote
If I shoot 40 different photos under different situations with ev comp set at 0 and 30 of them are underexposed I don't believe its a matter of being unfamiliar with the way a metering system works.Why would you not have the camera expose to get 30 of the 40 pictures correctly exposed and have maybe 10 overexposed? Even if I use center weighted metering I have to use + exposure compensation....Bob
It's being unfamiliar w/ the way THAT metering system works. Overexposure of film (and a large latitude in true iso ratings) was dealt with by having a 1/2 stop "fudge factor" built in. Pentax has carried this through their DSLR's and did Nikon for the most part. Just the way it is..
The NEW Nikons have a menu item (one sorely needed by Pentax) that allows a GLOBAL change to the metering baseline. Then you can produce the 126 peaks to your hearts content. Nikon, in the manual, does warn you that this is global and recommends sticking to EV adjustments on a picture by picture basis.
Out of curiosity please post one of these underexposed shots. It could be your meter is off but it's hard to tell from talk.
1 normal shot (preferably CW) and one "white wall" will paint the picture better.
One other aspect is that Pentax seems to be very conservative in their contrast curves.
Most exposures are more effectively adjusted by lowering the white point then by exposure compensation in post process. At least in my opinion.
My favorite quote from the guru of Leica Mr. Irwin Puts:
'The exposure meter is calibrated to some clearly defined standards and the user needs to adjust his working method and his subject matter to these values. It does not help to suppose all kinds of assumptions that do not exist.'
03-07-2008, 08:18 AM   #10
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QuoteOriginally posted by Lowell Goudge Quote
I can live with that, I am going by tests I have done, and the problem is that the difference is within 1/3 stop therefore it may be a question of being below the threshold of changing to the next 1/3 stop.
It's more like -.4375 stops below "center"(127.5-110= 17.5: 17.5/40 approx). 40 "points is roughly a full stop in that part of the histogram (ends are non-linear). And to state it as Ms. Borg put it "110 in sRGB color space, gamma 2.2."

Sorry just spent Waaay to much time looking into meters ect. when I was in my "why does my *ist-D underexpose" phase...........
Technically my D exposes a white wall at about 90. And this is after re-calibration by Pentax.
Personally this is a bit low but I live by the Puts philosophy (stated above in an earlier post) and as long as I understand it, it's easy to deal with. If any camera of Pentax can be accused of "wonky" metering it's that one.....
As a side note, just ran across a nice article dealing w/ ETTR:
quote:
...in the final analysis, ETTR isn’t about overexposure, but rather proper exposure, while avoiding true highlight clipping of linear-encoded data. This often isn’t the exposure our light meters recommend.
Exposing for RAW | Digital Photo Pro Magazine
03-07-2008, 09:25 AM   #11
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QuoteOriginally posted by jeffkrol Quote
It's more like -.4375 stops below "center"(127.5-110= 17.5: 17.5/40 approx). 40 "points is roughly a full stop in that part of the histogram (ends are non-linear). And to state it as Ms. Borg put it "110 in sRGB color space, gamma 2.2."

Sorry just spent Waaay to much time looking into meters ect. when I was in my "why does my *ist-D underexpose" phase...........
Technically my D exposes a white wall at about 90. And this is after re-calibration by Pentax.
Personally this is a bit low but I live by the Puts philosophy (stated above in an earlier post) and as long as I understand it, it's easy to deal with. If any camera of Pentax can be accused of "wonky" metering it's that one.....
As a side note, just ran across a nice article dealing w/ ETTR:
quote:
...in the final analysis, ETTR isnít about overexposure, but rather proper exposure, while avoiding true highlight clipping of linear-encoded data. This often isnít the exposure our light meters recommend.
Exposing for RAW | Digital Photo Pro Magazine
As I said you need to look at the contrast setting. a grey scale of 40 is 1 stop on minimum contrast, but grey scale of 50 is 1 stop on maximum contrast. I actually checked this out by using a lens to measure the whole dynamic range.

but you get the idea, depending on whether your camera is set to 1/3 or 1/2 increments for exposure, as you click through apature stops you sometimes see a large jump. My feeling is for automatic apature lenses, you can live with 1/3 setting because the camera controls this, but with manual apature l;enses, I believe you are better off with 1/2 stop, so the metering is working in steps that are consistent with what you change on the lens.

As far as *istD under-exposing, mine does not, K10 may over expose very slightly 1/3 stop but I don't have a calibrated light source to prove this., both cameras with same (AE capable) lens, same day, same contrast setting have within 10 points grey scale. My only issue with the K10D is the manual apature metering
03-07-2008, 10:22 AM   #12
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jeff, they should collect your posts in this thread and make a "sticky" thread on camera light metering.
03-07-2008, 12:23 PM   #13
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QuoteOriginally posted by PentaxPoke Quote
jeff, they should collect your posts in this thread and make a "sticky" thread on camera light metering.
Sticky things attract flies
03-07-2008, 03:24 PM   #14
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QuoteOriginally posted by jeffkrol Quote
Sticky things attract flies
Exactly! Catch them with the sticky fly tape, then there will be less threads entitled "The PeNikCanSonOly xxx-D DSLR under/over exposes" It is a common thread on camera forums.
03-07-2008, 03:37 PM   #15
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QuoteOriginally posted by PentaxPoke Quote
Exactly! Catch them with the sticky fly tape, then there will be less threads entitled "The PeNikCanSonOly xxx-D DSLR under/over exposes" It is a common thread on camera forums.
and exactly where do you propose to put them once caught?
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