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09-28-2009, 11:53 PM   #1
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What constitutes correct exposure?

I would welcome the comments of our members on this topic.
Many posts have claimed that the K20 overexposes.
My experience contradicts this. I follow the ETTR rule with the proviso the highlights with the exception of spectral highlights (reflections) should NOT be clipped.
The image on the LCD screen mat appear too bright, but who cares, The camera previews using the JPG settings selected in your setup. This will deliver an image with little of no shadow clipping.
All of my exposures are in Manual, PEF format. DNG converter (Free) converts to DNG for processing in LR2.
You decide after the event how much shadow detail you want to have.

09-29-2009, 12:00 AM   #2
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My experience with the *istD, K10 and K20 was that exposure was just plain all over the place if the meter was trusted.
Thankfully, they seem to have gotten it right with the K-7
09-29-2009, 01:19 AM   #3
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QuoteQuote:
All of my exposures are in Manual, PEF format. DNG converter (Free) converts to DNG for processing in LR
Just a quick question photog, was wondering why you record the images in PEF format then convert? I record in DNG which imports straight into LR, just wondered if I was missing something?
09-29-2009, 04:48 AM   #4
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I frankly like the exposure of the K20 pretty well. It significantly over exposes compared to my K10, but I guess I would describe that as the K10 under exposing and not the other way around. If I want the two to be equivalent, I would have to do a minimum of .3 EV compensation and probably closer to .6.

09-29-2009, 07:34 AM   #5
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I found my K10D tends to slightly underexpose most of the time. It's easy enough to adjust for. It does seem to vary slightly with different lenses, especially manual lenses. I would estimate that 3/4 of the outside photos I shoot are around water or snow and those conditions will play havoc with any light meter or camera. I've learned for the most part how to tweak my settings to get what I want. I will say that even left to the default settings there were very few shots that I couldn't fix in PP rather easily.
09-29-2009, 08:19 AM   #6
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The answer to this question is exactly as subjective as it was in the last thread on this exactly this topic. The correct exposure is the one you want. Of course, no camera can predict that, so the correct exposure in practice is the one that meets ISO standards for how bright to expose a grey card. When shooting anything but a gray card, there is basically no single answer. ETTR is definitely *not* the definition of correct exposure, though - it's just one person's (well, lots of people's) opinion on how they personally *want* the exposure to come out. But one would normally expect to need to override the camera's suggested exposure much of the time to get an ETTR exposure.

As for why to shoot PEF then convert, saving space on the card is the usual reason - several Pentax models compress PEF files but not DNG.

Last edited by Marc Sabatella; 09-29-2009 at 11:22 AM.
09-29-2009, 08:59 AM   #7
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Correct exposure is when the picture (as defined by the area measured by the meter; spot, center, matrix) matches 18% gray.

That is all that the meter can do, get the exposure as close as it can to match 18% gray.

Now, most subjects aren't 18% gray, or look good exposed for 18% gray. White skin is closer to 12% gray, black skin is around 20-23% gray. Snow is white. Black fur is black.

The 'correct' exposure is the one that gives you the picture you want.
09-29-2009, 09:00 AM   #8
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For me, it's simple.

correct exposure is when I point the camera (in spot mode) at something that is mid grey, and it is in the middle of the histogram, or slightly below middle

I think pentax sets the metering to between 110 and 120 greyscale, there was a post about this a while back.

From then on, what you do with exposure is an individual's "artestic" selection.

If you know that the camera will produce this, you can safely go +2 stops and have full detail, above 3 stops it starts to degrade a little, and above 4.5 stops the highlights are completely blown out, A similar behavior exists below for under exposure

This is based upon imperical data obtained by plotting the histogram values as a function of F stops above and below what the camera thought was Ideal metering on a uniform surface.

Anyone who does this simple test will then be able to understand the exposure range of your camera and make judgements based upon spot metering.

I will agree however that I have found metering at times a little suspect on my *istD and K10D, if I let the camera in fully control exposure and as wheatfield has indicated, the K7D appears much better. This might be somethign to do with a change from 11 metering points to 77

09-29-2009, 12:37 PM   #9
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There's no 'correct' exposure to me - just bad, good and better, judged on how the details of the subject matter in the image has been rendered.

Brian Peterson explains it well in his book 'Understanding Exposure'

As for the K10D and K20D, Pentax have been known to try and avoid clipping highlights in their auto metering. This is a plus for me, but I do tend to need a small boost in EV at times to get exposure right for me on both the K10D and K20D.
09-29-2009, 10:42 PM   #10
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ozlizard, I shootin PEF the native format as it reduces the processing time in camera a little. Conversion with DNG converter reduces file siz on HDD by about 40%
09-30-2009, 10:49 AM   #11
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From a purely technical perspective, correct exposure when shooting with a digital camera is when everything falls within the range of the histogram with no detail lost. It's all relative though and the idea of good exposure reminds me of that of good composition. During a photo club outing last spring a couple of fellow members asked how I can determine correct exposure outdoors in full sun when I'm wearing sunglasses. I responded that my sunglasses have never stopped me from getting good exposures when I shoot film. Why would digital capture be any different?

Ansel Adams once said that as he grew older he found his early prints to be too light in tone. During the late 1950's he went back to his early negatives and reprinted many of them much darker. It's interesting to see these later prints and how they stand up compared to his early ones from the same negatives.
09-30-2009, 11:24 AM   #12
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in simplier terms, correct exposure is normal or balanced exposure. a correctly exposed photo should not be too overexposed enough to wash out the details or the right intensity of color/tone of the photo and should not be underexposed enough to hide or remove the essential details of the photo.

there are situations were there are tendency or to deliberately underexpose or overexpose the photo to some extent inorder to produce a certain result. the problem is that there is a tendency of overdoing it as well.

the thing is, knowing and achieving correct exposure has always been a problem to photographers, especially for the beginners. the obvious type would be having an underexposed/overexposed subject. now a photo does not only concentrated on the subject's exposure alone, it should also include the 3 parts of the photo; foreground, middleground and background. a rather argumentative question should be answered like,
you would think that you had attained the correct exposure for your subject (middleground), but is your background's exposure isn't washed out or too dark?
09-30-2009, 11:49 AM   #13
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QuoteOriginally posted by Pentaxor Quote
in simplier terms, correct exposure is normal or balanced exposure. a correctly exposed photo should not be too overexposed enough to wash out the details or the right intensity of color/tone of the photo and should not be underexposed enough to hide or remove the essential details of the photo.

there are situations were there are tendency or to deliberately underexpose or overexpose the photo to some extent inorder to produce a certain result. the problem is that there is a tendency of overdoing it as well.

the thing is, knowing and achieving correct exposure has always been a problem to photographers, especially for the beginners. the obvious type would be having an underexposed/overexposed subject. now a photo does not only concentrated on the subject's exposure alone, it should also include the 3 parts of the photo; foreground, middleground and background. a rather argumentative question should be answered like,
you would think that you had attained the correct exposure for your subject (middleground), but is your background's exposure isn't washed out or too dark?
Sadly, life is not that simple and scenes generally have more exposure lattitude than the recording medium, be it film or a digital sensor. As I stated, the only thing that is correct, is if what you the photographer want to be exposed is at the part of the histogram you want it to be.
09-30-2009, 04:35 PM   #14
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QuoteOriginally posted by Lowell Goudge Quote
Sadly, life is not that simple and scenes generally have more exposure lattitude than the recording medium, be it film or a digital sensor. As I stated, the only thing that is correct, is if what you the photographer want to be exposed is at the part of the histogram you want it to be.
that is another dilemma that is encountered by photographers. other than that, it's user-error.
09-30-2009, 05:11 PM   #15
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Correct exposure = L*50 @ 18% gray

Well, technically speaking, "correct" exposure would place a L*a*b* value of L*50 a*0 b*0 on an 18% gray card (note: Kodak 18% "Gray" Cards are *not* gray). To check this, expose an 18% gray card at various exposure values (auto-bracket 5 shots in 1/3 stop increments for example) and check it in Photoshop. With your info palette set to read out in L*a*b*, find the exposure that gives you L*50 on the 18% gray card. For various RGB working spaces, L*50 would be...
sRGB: R=G=B, 119 +/-2
AdobeRGB(98): R=G=B, 118 +/-2
ProPhotoRGB: R=G=B, 100 +/-2

The exception to this would be if this results in diffuse (detail) highlights that are blown out....but if that were the case, I'd be looking for other things that would be causing that like incorrect in-camera JPEG settings or incorrect settings in your RAW/DNG convertor.

On the other hand, if this results in too-dark highlights, then you could expose for the highlights (ETTR philosophy) and let the 18% gray fall where it may. As long as the 18% gray photographs to *light* (L*>50) with correct exposure for the highlihts, you'll have overall better shadow detail and less noise in the shadows.

I've got a project in mind where I'm going to be adjusting brightness/contrast and possibly tone curve controls in Lightroom to get the gray patches on a Macbeth ColorChecker mapped out exactly correct....and then I'll see what sort of picture this produces with the gray patches reproducing more technically correct. My guess is much flatter than I'm used but with possibly much improved highlight rendering/smoothness. We'll see.

Regards,
Terry
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