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09-06-2010, 08:48 AM   #16
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QuoteOriginally posted by lol101 Quote
What I am talking about is K10 rendition of a sunny day where you get dark blue skies with grey clouds (histogram bunched to the left) instead of light blue skies with white clouds (full histogram representing exactly the luminance gradations from dark to light tones, as a handheld meter would give you).

A correct exposure in my book is when whites are rendered white (not grey) and blacks black.
I am with you here. It may not have been clear from my earlier post, but the captured image is shifted left even in M mode with settings from an accurate hand-held meter. Clearly the image processor is doing something here. Either that or the stop-down mechanism and/or shutter on my camera is not working properly.


Steve

09-06-2010, 09:18 AM   #17
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QuoteOriginally posted by lol101 Quote
What I am talking about is K10 rendition of a sunny day where you get dark blue skies with grey clouds (histogram bunched to the left) instead of light blue skies with white clouds (full histogram representing exactly the luminance gradations from dark to light tones, as a handheld meter would give you).

A correct exposure in my book is when whites are rendered white (not grey) and blacks black.
QuoteOriginally posted by stevebrot Quote
I am with you here. It may not have been clear from my earlier post, but the captured image is shifted left even in M mode with settings from an accurate hand-held meter. Clearly the image processor is doing something here. Either that or the stop-down mechanism and/or shutter on my camera is not working properly.


Steve
Sorry guys....... that's just incorrect and no, most likely there is nothing wrong w/ the camera......
QuoteQuote:
Effect of Meter Calibration—Reflected-Light Meters
The effect of most reflected-light meter calibrations is to give whatever is metered an ex-posure somewhere near the middle of a film’s exposure range, although it’s seldom at the exact midpoint. If the area metered is close to a medium reflectance, the exposure for that area usually will be satisfactory. The greater problem usually is in getting satisfactory exposure for light and dark areas. The effect of meter calibration on light and dark ele-ments of a subject perhaps is best visualized by superimposing those exposures on the film’s characteristic curve.
http://www.largeformatphotography.info/articles/conrad-meter-cal.pdf
A mild reminder, this is for film not digital sensors which have different characteristics...
http://www.libraw.org/articles/zone-v-in-digital.html
http://www.libraw.org/articles/Canon-5Dmk2-headroom.html
And for fun..........
http://www.libraw.org/articles/magenta-filters-on-digicam.html

Last edited by jeffkrol; 09-06-2010 at 09:30 AM.
09-06-2010, 09:50 AM   #18
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QuoteOriginally posted by lol101 Quote
What I am talking about is K10 rendition of a sunny day where you get dark blue skies with grey clouds (histogram bunched to the left) instead of light blue skies with white clouds (full histogram representing exactly the luminance gradations from dark to light tones, as a handheld meter would give you).
Which handheld meter does that, and in what conditions? An incident-light meter might, but a reflected-light meter would typically behave otherwise - and that's what DSLR's have,

Basically, you are describing the exposure you prefer - and that's common. But this is not *correct* exposure. Correct exposure of a solid bue sky should have the histogram somewhat left of center. A few white clouds shouldn't necessary change that either way. If the sky is mostly white clouds, then *they* should end up slightly left of center, and the blue that much further left.

These are "correct" exposures, but they aren't t necessarily the exposures you might *want*. And that's why exposure compensation was invented - to allow you to get the exposure you *want* even though "correct" exposure differs.

QuoteQuote:
A correct exposure in my book is when whites are rendered white (not grey) and blacks black.
Your book, however, is not what camera manufacturers are compelled to follow. ISO has produced standards for camera exposure, and they specify things work as I've described. *That* is the book followed by camera manufacturers.

And really, when you think about it, it's *impossible* for a reflected-light meter like that in the camera to render white as white and black as black in all or even sot cases. A plain sheet of white paper versus a plain sheet of black paper - a camera has *no idea whatsoever* that these are in fact different sheets of paper. As far as the meter is concerned, both are just as likely to be a sheet of gray paper in good light (the one that appears white to our eyes) versus a sheet of gray paper in poor light (the one that appears black to our eyes). All of these would reflect exactly the same amount of light to the meter, and that's why they all get metered the same way by any reflected-light meter. Only an incident-light meter would be able to tell the difference and meter the sheets of paper as you suggested.

This is essential to understand if you wish to be able to work with your camera's reflected-light meter. and not constantly wonder why it doesn't do what you expect. It does pretty much *exactly* what you expect if your expectations are set by science and ISO standards rather than your subjective impressions of what you might "want".
09-06-2010, 10:20 AM   #19
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Interesting thread but I wonder what some of the posters would make of my experience with one of my K10D bodies. When it came back from Pentax repair (focus issue, which was fixed) it consistently underexposed by about 1 stop in any meter mode, exposure mode, and any subject. Previously it was pretty much on the money as is my other body which has never been in for any repair. Why? Other than the repair, the only other thing Pentax did (as far as I know) was upgrade the firmware to version 1.30.

Richard

09-06-2010, 01:20 PM   #20
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QuoteOriginally posted by Old Timer 56 Quote
Interesting thread but I wonder what some of the posters would make of my experience with one of my K10D bodies. When it came back from Pentax repair (focus issue, which was fixed) it consistently underexposed by about 1 stop in any meter mode, exposure mode, and any subject. Previously it was pretty much on the money as is my other body which has never been in for any repair. Why? Other than the repair, the only other thing Pentax did (as far as I know) was upgrade the firmware to version 1.30.

Richard
Just for clarity... what model is your other body? what was the major repair?
almost sounds like they knocked the repaired one out of speck... or the possibility it was out of speck to begin with regardless of the "outcome"......
Just shoot a white wall w/ everything set to neutral (contrast ect)
If the peak response it around 110 RGB color space in spot or cw the camera is behaving as it should.. As to Matrix, well there is a lot of leeway here for manufacturers and s such it is almost impossibe to determine why it does what it does. A white wall should still be within 1/2 stop of the 110... 40 points in the mid level of the histogram is roughly 1 stop. More precisely though I deem 10 points (1/4 stop) well within any statistical error.......
QuoteQuote:
Now let's switch to full Adobe RGB (1998), which is gamma=2.2 space, and enter L values to get RGB.

L=43 -> RGB=101
L=58 -> RGB=138
L=77 -> RGB=189
L=100 -> RGB=255 (I have not checked this, sorry).

So, in the perfect world of a spot-meter calibrated to ISO standard and pure gamma = 2.2 transform of perfectly linear data coming from the sensor, the neutral surface should render 101 RGB if exposed according to the spot-meter; next stop is 138 RGB, then comes 189 RGB, and finally we are getting clipping increasing exposure full 3 stops instead of 2.97 stops which are the theoretical limit as it was shown above.
09-06-2010, 01:44 PM   #21
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QuoteOriginally posted by jeffkrol Quote
Just for clarity... what model is your other body? what was the major repair?
almost sounds like they knocked the repaired one out of speck... or the possibility it was out of speck to begin with regardless of the "outcome"...........
Both bodies are K10D. The one that went to Pentax repair backfocused, at least with the lens I mainly used on it - the 21mm DA. They fixed that and I have no more focus problems. But I want to reiterate that exposure was fine before Pentax repair got their hands on it.

I suppose I might have sent the body back to them but did not want to risk damage in transit nor having Pentax mess up something else. The fix for the underexposure problem is simple - set exposure comp to +1. I mostly use AV mode except when shooting with an off-camera flash (Vivitar 283) triggered by the built-in flash. then it's in M. Exposure is fine with that setup but the 283 is set at one of the Auto modes and that pretty much takes care of the exposure. I tried a few shots in M without any flash and the camera still underexposes about 1 stop unless I compensate by overexposing by 1 stop.

It seems that the issue is with the K10D meter system, at least after Pentax repair "fixed" it.

Richard
09-07-2010, 04:09 AM   #22
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QuoteQuote:
Which handheld meter does that, and in what conditions? An incident-light meter might, but a reflected-light meter would typically behave otherwise - and that's what DSLR's have,
I am referring to an incident light-meter which is what I use commonly.

QuoteQuote:
Basically, you are describing the exposure you prefer - and that's common. But this is not *correct* exposure. Correct exposure of a solid bue sky should have the histogram somewhat left of center. A few white clouds shouldn't necessary change that either way. If the sky is mostly white clouds, then *they* should end up slightly left of center, and the blue that much further left.
I just can't see how the composition of a scene (wether or not it has clouds, brick walls, trees or red cars in it) can influence the "right" exposure...

Furthermore, the correct exposure for white clouds is the one that renders them... white. If I follow you, you're saying that white clouds should end up slightly left of center (ie slightly under middle grey) which should render them as darkish grey. How can this be considered "correct"?



Or did you mean that if I am using a "dumb" reflective meter such as spot metering, it is the result I should get?

In the later case, I agree but we are talking about evaluative metering and the whole purpose of it is that it is supposed NOT to act like a dumb reflective meter.

One ISO value + one aperture value = one shutter speed value for the correct (in the sensitometric sense) exposure.

Then I might want the scene to appear clearer or darker but that has nothing to do with the meter giving me the "correct" exposure for starter.

QuoteQuote:
These are "correct" exposures, but they aren't t necessarily the exposures you might *want*. And that's why exposure compensation was invented - to allow you to get the exposure you *want* even though "correct" exposure differs.
OK, I think I get that...

QuoteQuote:
Your book, however, is not what camera manufacturers are compelled to follow. ISO has produced standards for camera exposure, and they specify things work as I've described. *That* is the book followed by camera manufacturers.
QuoteQuote:
And really, when you think about it, it's *impossible* for a reflected-light meter like that in the camera to render white as white and black as black in all or even sot cases. A plain sheet of white paper versus a plain sheet of black paper - a camera has *no idea whatsoever* that these are in fact different sheets of paper. As far as the meter is concerned, both are just as likely to be a sheet of gray paper in good light (the one that appears white to our eyes) versus a sheet of gray paper in poor light (the one that appears black to our eyes). All of these would reflect exactly the same amount of light to the meter, and that's why they all get metered the same way by any reflected-light meter. Only an incident-light meter would be able to tell the difference and meter the sheets of paper as you suggested.
Matrix metering is supposed to work differently than that although it would probably fail the white sheet of paper test.

Nevertheless, a good matrix meter should be able to do a resonably good job in most cases documented in the camera internal database. How do I know? Well, I have several cameras that seem to work it out... the K10 not being one of them

QuoteQuote:
This is essential to understand if you wish to be able to work with your camera's reflected-light meter. and not constantly wonder why it doesn't do what you expect. It does pretty much *exactly* what you expect if your expectations are set by science and ISO standards rather than your subjective impressions of what you might "want".
If you were right, all cameras would expose the same in matrix/evaluative metering since they would all be based upon the same "science and ISO standards". But the fact of the matter is: they don't and some do a better job than others, probably just because of better programming and more extensive databases of "photographic situations".
09-07-2010, 09:07 AM   #23
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QuoteOriginally posted by lol101 Quote
I just can't see how the composition of a scene (wether or not it has clouds, brick walls, trees or red cars in it) can influence the "right" exposure...
Because the composition of a scene changes the amount of reflected light. You can't expect a DSLR to act as an incident light meter - it's not going to happen.

QuoteQuote:
we are talking about evaluative metering and the whole purpose of it is that it is supposed NOT to act like a dumb reflective meter.
True, but the whole evaluative metering process is more of an art than a science. There is no way to objectively say for certain how any given exposure should turn out. That's one reason I dumped multsegment metering years ago - while it often guessed well, it also often didn't, and it's hard to preidct when it will do what. I find center-weighted metering far more useful. It's at least as likely to end up giving the subjectively "right" answer, and more importantly, it's also much easier for me to anticipate when it won't and preemptively act accordingly.

QuoteQuote:
If you were right, all cameras would expose the same in matrix/evaluative metering since they would all be based upon the same "science and ISO standards".
Not at all - as I said, it's only flat featureless expanses that have a guaranteed "correct" according to standards result. The minute a scene has any variation, then that introduces an element of subjectivity. One matrix meter might happen to think one of the lighter areas is most important and therefore strive to expose it to an "average" brightness; another might think one of the darker areas is most important and strive to render that as average - so the resulting exposures will differ.

QuoteQuote:
But the fact of the matter is: they don't and some do a better job than others, probably just because of better programming and more extensive databases of "photographic situations".
And also because the definition of "better" here is extremely subjective. Consider the case of a scene involving brightly lit areas and dark shadow areas. The camera cannot redner the same amount of detail in both. It has to make a choice - render more detail in the lights, render more details in the shadows, or try to compromise and thus not render optimally in either area. And it's impossible to say which is "right". Depending on the scene and what the particular photographer in question wants the image to look like, any of the above could be "right:. So a matrix meter has to guess, and no matter which way it guesses, it will necessarily end up being "right" for some and "wrong" for others.

Bottom line: matrix metering is inherently subjective, and hence usually harder to predict. If you want predictability, swithc to center-weighting.

09-07-2010, 06:55 PM   #24
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My K10D underexposes most of the time in matrix metering

I echo thge previous comments that say matrix metering & AF is a weakness in k10D. I have the Tamron 28-75mm and for the same apertures, I can see that pix are not 100% sharp in indoors (I bump up ISO to 640-800) to improve the shutter speed (around 1/40 -1/60) second but lots of pix (not all) are not sharp. I always use center point in focus
In the exposure, I use spot metering rather than matrix all the time. Even in spot metering, I found the "spot" is slightly big so I need to review the images and check the histogram and readjust the shot
Matrix metering is not intelligent in tricky scenes
I guess I need to decouple AF point and exposure and use AF button to lock focus and use the shutter button to just measure exposure... There is a lot to learn, its also fun but when you see other cameras doing it with minimal intervention in P mode, it is sometimes dispiriting
But Pentax got some useful modes liek Sv mode, in Indoors I find it to be very useful.

I am keenly watching new arrivals, let us see how the feedback is....
09-08-2010, 03:06 AM   #25
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I find my k10d underexposes for my liking be default. I have always assumed it does this to protect the highlights - and when I shot RAW I left it alone and bumped up any exposures as needed in PP.

Since my daughter was born I take more pictures and have less time, so I tend to shoot JPEG these days, preferably with the results being as near to as I want them straight from the camera. To that end I have sharpness and saturation bumped up a notch, and I generally have the exposure compensation set to +1 stop.

I use P mode most of the time these days, and I've customised it so the front dial is program shift and the back dial is exposure compensation - so if I know the camera is going to go one way or the other exposure-wise (if there is a lot of sky, for example) I can dial in more or less compensation without moving the camera. I use the matrix metering usually.

Anyway, my point is that there is no such thing as 'correct exposure' in the absolute sense, it's all about the effect you are trying to achieve. I have numerous shots of my daughter where the highlights are blown, but in most cases that was what I wanted (and in some it was a happy accident!) and equally I have shots that are 'underexposed' in the sense that they are darker than the scene I was looking at - but again it was the effect I wanted.

It's easy to adjust in camera (having two dials is one of the best features of the K10d, and the one I would miss most) and in PP. It's just about knowing what you want, and how/why the camera might try and stop you doing that by trying to second-guess what you're doing.

For my preferences, the meter is generally about a stop under - but as I said I have +1 stop permanently dialled in, so it's no problem.
09-08-2010, 07:46 PM   #26
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QuoteOriginally posted by Marc Sabatella Quote
It's normal for people to expect a sunny day

None of this is K10D specific - it's common to pretty much all cameras that aren't specifically designed for beginners. Cameras specifically designed for beginners do often try to make
"guesses" as to what you want and will deliberately overexpose portions of the picture or deliberately reduce the contrast in the scene to avoid these problems. But most SLR's expect you to take control and make those adjustments yourself as you see fit.

.
Then what is the idea of having a "GREEN MODE" In green mode you have no possibility to change any parameter so the idea should be that the camera choose a reliable exposure. My experience with K10D is not the case.
09-09-2010, 08:00 AM   #27
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Read the rest of my posts where I explained why a camera *cannot* possibly read your mind about the exposure you want. It tries to guess, but can't always guess right. That's one of the main reasons why I also recommend people skip Green mode and use P instead.
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