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Author Topic: lower EC or ETTR?  (Read 24750 times)
Graystar
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« Reply #60 on: August 15, 2012, 01:22:58 PM »
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Yes, 1.5 stops OVER what the incident meter suggested (ETTR) with raw normalization that shows zero blown highlights.
And what did the camera meter suggested?

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The JPEG I’m referring to is the camera generated JPEG that would be totally blown out using that meter suggestion. You can’t expose for raw and JPEG the same way. One major reason is the processing which I continue to ask: how can we separate that from the discussion and process. The JPEG processing is in-camera, the raw under my control. One is a useless exposure, the other is pristine with far less noise due to ETTR.
Well..."far less" might be a stretch...but anyways, I'm not sure why we're concerned about the in-camera JPEG to begin with.
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digitaldog
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« Reply #61 on: August 15, 2012, 01:26:59 PM »
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And what did the camera meter suggested?

Probably something equally wrong (considering I was metering with an Incident meter) <g>. Plus I was shooting flash. The images can be seen here (page 4):
http://www.digitalphotopro.com/technique/camera-technique/exposing-for-raw.html

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Well..."far less" might be a stretch...but anyways, I'm not sure why we're concerned about the in-camera JPEG to begin with.

And yet, that is exactly what the meter is aiming for along with a defined and understood processing.
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Andrew Rodney
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deejjjaaaa
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« Reply #62 on: August 15, 2012, 02:10:16 PM »
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When metering under tungsten light, if I increase exposure by 1/3rd stop over standard exposure, I will clip the green in bright white objects.  So my Nikon, at least, doesn't underexpose in tungsten light.
no Graystar - I was referring to my question/note to Guillermo (see what I was answering above), who was essentially saying that spot metering is not necessary... he saying basically that matrix metering or centerweight metering will be good and I was saying that such metering will underexpose under the tungsten light... he knows that for sure, but his position is (I guess) that w/ modern sensors and raw converters that is OK and we do not need to put any expo correction for such metering in camera under such light...
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bjanes
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« Reply #63 on: August 15, 2012, 02:38:06 PM »
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Yes, 1.5 stops OVER what the incident meter suggested (ETTR) with raw normalization that shows zero blown highlights.

The JPEG I’m referring to is the camera generated JPEG that would be totally blown out using that meter suggestion. You can’t expose for raw and JPEG the same way. One major reason is the processing which I continue to ask: how can we separate that from the discussion and process. The JPEG processing is in-camera, the raw under my control. One is a useless exposure, the other is pristine with far less noise due to ETTR.

The DigitalDog is correct: calibration of the meter and calibration of the sensor are two separate and essential components that govern sensor saturation for a given light meter reading determined exposure. Reflected light meters are governed by ISO 2720:1974 (see Wikipedia). The sensor calibration is governed by ISO 12232:2006 (again see Wikipedia). If the saturation standard is used (as with DXO measurements), exposure of an 18% reflectance card will give 12.7% sensor saturation. This allows 0.5 EV highlight headroom. However, some manufacturers wish to provide more headroom. This could be accomplished by changing the calibration of the meter or the sensor. Changing the calirbration of the meter would cause conflicts with external meters, so the sensor calibration is usually changed.

Phase One backs allow a great deal of headroom as shown by the sensor DXO ISO measurements for Phase One sensors. A light metered exposure of a gray card would give much less than 12.7% saturation. If the raw file is rendered, the tone curve used by the raw developer or in camera JPEG engine also comes into play.

With my Nikon D3 a metered exposure of a gray card gives close to 12.7% saturation, but my D800 gives closer to 15% saturation. ACR 7.1 and LR 4.1 with PV2012 use hot tone curves, and the rendered sRGB values are considerably greater than the expected value of 118.
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Graystar
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« Reply #64 on: August 15, 2012, 04:21:40 PM »
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If the saturation standard is used (as with DXO measurements), exposure of an 18% reflectance card will give 12.7% sensor saturation. This allows 0.5 EV highlight headroom.

Actually, exposure of any value of reflectance will give 12.7% saturation.  It's the fact that you used an 18% card that will give you 0.5 EV "headroom", which is the same as being 0.5 EV underexposed.  If you used a 25% card you'd have 1.0 EV of headroom.  But this idea of headroom is questionable, as the most common 18% card, the Kodak, comes with instructions to increase exposure by 0.5 EV.  So anyone using an 18% card as instructed has no headroom.

If the D800's metering point provides 15% saturation then I hope there's an instruction somewhere to disregard Kodak's instructions...otherwise anyone who doesn't will be clipping his whites and not understanding why (other than the obvious "this is not a film camera.")
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deejjjaaaa
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« Reply #65 on: August 15, 2012, 04:28:07 PM »
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Actually, exposure of any value of reflectance will give 12.7% saturation.  It's the fact that you used an 18% card that will give you 0.5 EV "headroom", which is the same as being 0.5 EV underexposed.  If you used a 25% card you'd have 1.0 EV of headroom.  But this idea of headroom is questionable, as the most common 18% card, the Kodak, comes with instructions to increase exposure by 0.5 EV.  So anyone using an 18% card as instructed has no headroom.

If the D800's metering point provides 15% saturation then I hope there's an instruction somewhere to disregard Kodak's instructions...otherwise anyone who doesn't will be clipping his whites and not understanding why (other than the obvious "this is not a film camera.")

that is why particular camera model has to be tested and not assumed that its spot meter will be giving 12.x%
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Graystar
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« Reply #66 on: August 15, 2012, 06:27:53 PM »
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that is why particular camera model has to be tested and not assumed that its spot meter will be giving 12.x%
That would only be for ETTR practitioners.  For everyone else, all that matters is the unprocessed sRGB values.

When a D800 spot meters and photographs an evenly lit neutral surface...if the resulting image, demosaiced and white balanced only, reads 100, 100, 100 in the metered area, then it meters just like every other Nikon.  I would be surprised if it didn't.  If it does, then the Kodak gray card and instructions will work just fine.
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bjanes
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« Reply #67 on: August 15, 2012, 10:23:38 PM »
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That would only be for ETTR practitioners.  For everyone else, all that matters is the unprocessed sRGB values.

When a D800 spot meters and photographs an evenly lit neutral surface...if the resulting image, demosaiced and white balanced only, reads 100, 100, 100 in the metered area, then it meters just like every other Nikon.  I would be surprised if it didn't.  If it does, then the Kodak gray card and instructions will work just fine.


Again, you are confusing the meter reading, which would give an f/stop and shutter speed for a given ISO. How the sensor would respond to this exposure is a different matter. According to the REI (recommended exposure index) that Japanese manufactures use, they may assign whatever sensor ISO they want, and the resulting sensor saturation may or may not be 12.7%. In your earlier posts you made some good points, but more recently you have gotten off track. Please read up on these topics before posting again. Doug Kerr has a good paper on the subject.

To determine the sensor saturation, one has to look directly at the raw file with a program such as Rawdigger. The first step is to determine the saturation value, which may not be 2^14 -1 (16383) for a 14 bit ADC. One then determines the raw value for the exposure (the ISO mentions an 18% card, but any uniform target (gray or white) will do as you mentioned. One may have to subtract an offset (Canon cameras). The quotient of these values is the percent saturation. The rendered sRGB value can not be used since a tone curve may have been applied.


DXO describes how they determine sensor sensitivity and how the manufacturer may deviate from the saturation standard. Look at the ISO measurement for the Phase One IQ180.

Regards,
Bill
« Last Edit: August 16, 2012, 06:11:38 AM by bjanes » Logged
Graystar
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« Reply #68 on: August 16, 2012, 02:14:02 PM »
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Again, you are confusing the meter reading, which would give an f/stop and shutter speed for a given ISO. How the sensor would respond to this exposure is a different matter. According to the REI (recommended exposure index) that Japanese manufactures use, they may assign whatever sensor ISO they want, and the resulting sensor saturation may or may not be 12.7%. In your earlier posts you made some good points, but more recently you have gotten off track. Please read up on these topics before posting again. Doug Kerr has a good paper on the subject.

To determine the sensor saturation, one has to look directly at the raw file with a program such as Rawdigger. The first step is to determine the saturation value, which may not be 2^14 -1 (16383) for a 14 bit ADC. One then determines the raw value for the exposure (the ISO mentions an 18% card, but any uniform target (gray or white) will do as you mentioned. One may have to subtract an offset (Canon cameras). The quotient of these values is the percent saturation. The rendered sRGB value can not be used since a tone curve may have been applied.


DXO describes how they determine sensor sensitivity and how the manufacturer may deviate from the saturation standard. Look at the ISO measurement for the Phase One IQ180.

I'm not confusing anything.  You're the one who's confusing metering with response and processing.  You're doing this because you can only think it terms of ETTR.  But that's not how cameras are designed to be used.  Camera makers never intended photographers to base exposure from the un-demosaic values, as they provide no tools to access those values.

The meter doesn't produce an f/stop and shutter speed.  The meter combines a luminance reading with the ISO speed (the speed you select, not the REI) to produce an EV.  That EV is then biased by any EC that the photographer has applied.  Then the biased EV is passed to the camera's exposure program.   For example, if you're in Program mode then the EV is looked up on a chart (also considering focal length on some cameras) and then the camera sets the aperture and shutter listed for that EV.  That program-mode chart should be in the back of your camera manual.

Metering works exactly the same way in a digital camera as it does in a film camera, as it does across digital cameras.  My Canon compact, spot-metering my gray card, gives me the same exact exposure settings as my Nikon D90.  This is all defined by ISO 2721.  Metering has nothing to do with REI.

Once the image is captured, however, the camera maker has complete control over how the signals get processed.  This is where REI comes in.  REI is the equivalent of pushing/pulling film...the film has a rated speed (the ISO speed) but you can process it as if it were any other speed, depending on how you decided to expose the film.  REI is the same thing.  The manufacturers process the signals to produce, supposedly, a particular result...that result being an RGB image in the sRGB colorspace.  Although not explicitely defined for REI (it is for SOS,) the sRGB image should have 18% gray right at RGB 118 (referred to as the "standard level".)

By extension, that puts 12.7% gray at RGB 100.  As it is the expressed purpose of REI to match meters (see CPIA DC-004 Explanation) it is reasonable to expect that a meter with a K of 12.7 metering a 12.7% gray reference will produce an RGB image with values of 100.  The problem is accessing that image, as all cameras apply additional processing based on defaults, picture controls, HDR settings, etc.  So how to we see the base RGB image?  We use a RAW converter that allows us to demosaic the RAW and apply white balance and nothing else.

http://www.cipa.jp/english/hyoujunka/kikaku/pdf/DC-004_EN.pdf

Now...as to whether sRGB 100 actually represents 12.7% saturation of the sensor...that's a different topic.  sRGB 255 may not represent full saturation of the sensor, but it's close.  And again, actual full saturation is a concern of ETTR practitioners only. 

And yes, I've read DxO and many of Doug Kerr's papers...including the one you reference, as well as the one where his exposure test produced RGB 100, 100, 100.
http://dougkerr.net/pumpkin/articles/Scene_Reflectance.pdf

I see you edited your post and removed your erroneous comment about 18%.  I'm glad you corrected your error, but I suggest that next time you read up on these topics before posting.
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bjanes
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« Reply #69 on: August 17, 2012, 07:48:12 AM »
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Metering works exactly the same way in a digital camera as it does in a film camera, as it does across digital cameras.  My Canon compact, spot-metering my gray card, gives me the same exact exposure settings as my Nikon D90.  This is all defined by ISO 2721.  Metering has nothing to do with REI.

Again, you don't seem to understand that REI or any other ISO value for the sensor is needed to determine the EV of the exposure as determined by the light meter. This is why the Canon 5D Mark II yields only 7.5% sensor saturation as shown in the Libraw post which you have disregarded. Have you looked at your raw files, or are you just spouting theory that you do not understand?

And yes, I've read DxO and many of Doug Kerr's papers...including the one you reference, as well as the one where his exposure test produced RGB 100, 100, 100.
http://dougkerr.net/pumpkin/articles/Scene_Reflectance.pdf

You have read these articles, but your comprehension appears to be deficient. Further discussion with you is pointless, and I am out of here. Where is the kill button?

Bill
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Graystar
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« Reply #70 on: August 17, 2012, 10:23:09 AM »
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Again, you don't seem to understand that REI or any other ISO value for the sensor is needed to determine the EV of the exposure as determined by the light meter. This is why the Canon 5D Mark II yields only 7.5% sensor saturation as shown in the Libraw post which you have disregarded. Have you looked at your raw files, or are you just spouting theory that you do not understand?

Once again it is you who doesn't seem to understand what REI means.  The expressed purpose of REI is to produce exposures that match handheld meters.  From DCX400...

"Recommend Exposure Index is an exposure index corresponding to the average exposure in a focal plane recommended by camera (imaging system) vendors (manufacturers etc.) for the purpose of reference to the setting [of] an exposure index (film ISO speed value) when using a separate exposure meter or accessory strobe etc.."

"...when the aperture or shutter speed is to be obtained by using a reflective stand-alone exposure meter or accessory strobe, the average photometry values are used.  Adequate preset value of film sensitivity (exposure index) must be adapted to such equipment during photography, in which case the recommend value preset by the maker (in other words, the value to obtain the 'standard exposure' mentioned above) is the 'Recommend Exposure Index."

So the purpose of REI is to get digital cameras to produce the same results as film cameras when it comes to setting exposure via handheld meters (and also camera meters, I just didn't quote that part.) There is NOTHING in the REI definition relating to sensor saturation.

Still, it would be quite foolish of a manufacturer to design a camera such that 1 1/2 stops of DR are wasted, but yet produce JPEGs that have blown highlights.  Certainly my Nikon D90 does not work this way.  Sure, OOC JPEGs will clip before RAW does, but only by 1/5 stop or so.  And of course, that's only because they're in sRGB.  Set them to AdobeRGB and they clip less.  If we could set them to ProPhoto, they wouldn't clip at all.

And I didn't disregard the 5D test.  I noted that the conclusions drawn were unverified.


Quote
You have read these articles, but your comprehension appears to be deficient. Further discussion with you is pointless, and I am out of here. Where is the kill button?

I'll take that to mean that you photographed a gray card (or white wall) with your D800, saw that the metered areas of the images turned out to be 100, 100, 100 when using a neutral profile, and have no way to reconcile that result with your supposed 15% saturation...and are now looking for a way out.
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deejjjaaaa
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« Reply #71 on: August 17, 2012, 10:56:18 AM »
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I'll take that to mean that you photographed a gray card (or white wall) with your D800, saw that the metered areas of the images turned out to be 100, 100, 100 when using a neutral profile, and have no way to reconcile that result with your supposed 15% saturation...and are now looking for a way out.

BJanes - may be you can do a favor and post a raw file from D800 please...
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Graystar
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« Reply #72 on: August 21, 2012, 12:15:05 PM »
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BJanes - may be you can do a favor and post a raw file from D800 please...

Doesn't look like you're going to get one.  Might I interest you in some Nikon D90 RAW files?

Here are three RAW files from my Nikon D90.  These shots are of my gray card in the sun, blurred.  The filenames start with an underscore because the color space was set to Adobe RGB.

_DSC9254.NEF is straight spot metering.
_DSC9255.NEF is at +2.7 EC.  The green channel isn't clipped.
_DSC9256.NEF is at +3.0 EC.  Here, the green channel is clipped.

ftp://graystar.tftpd.net/

12.7% gray, increased by +3, is 101.6%...so it makes sense that clipping is occurring at +3.0 EC.

Knowing this allows me to easily ETTR by simply setting EC to +2.7 and spot-metering the brightest highlight of a scene that I want to retain detail.  I just spot check a few areas to see which is the brightest.  No histogram needed.  That said, I find it simply isn't worth the effort because most of the scenes I shoot have a bright highlight somewhere with detail I want to keep.
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bjanes
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« Reply #73 on: August 21, 2012, 05:47:43 PM »
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BJanes - may be you can do a favor and post a raw file from D800 please...

Certainly. I have been out of town, so hence the delay. If you have interesting observations, please post them on the forum.


Stouffer wedge with step 1 just short of clipping in green channels (5000K), :

https://www.yousendit.com/download/TEhXb3BBMm11Yk5jR01UQw

Garden shot with Zeiss 21 Distagon at f/8, ISO 100. Green channels 1 EV short of clipping:

https://www.yousendit.com/download/TEhXb3BPd0E4NVd4djhUQw

Regards,

Bill
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Graystar
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« Reply #74 on: August 22, 2012, 09:12:27 AM »
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BJanes - may be you can do a favor and post a raw file from D800 please...
If it's just any ol' RAW file from a D800 that you want, Imaging Resource has lots of them...

http://www.imaging-resource.com/PRODS/nikon-d800/nikon-d800THMB.HTM
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deejjjaaaa
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« Reply #75 on: August 22, 2012, 05:04:07 PM »
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If it's just any ol' RAW file from a D800 that you want, Imaging Resource has lots of them...

http://www.imaging-resource.com/PRODS/nikon-d800/nikon-d800THMB.HTM

I was talking about raw files to use for meter measurement as described in http://www.rawdigger.com/houtouse/lightmeter-calibration , so that you can see if D800 really meters like bjanes says or not...

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bjanes
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« Reply #76 on: August 22, 2012, 06:40:56 PM »
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I was talking about raw files to use for meter measurement as described in http://www.rawdigger.com/houtouse/lightmeter-calibration , so that you can see if D800 really meters like bjanes says or not...

Sorry, but I did not know what type of raw files you were seeking. I have uploaded files for calibration procedure to Usendit.

Img 1 is a white target exposed according to the meter. Illumination was Solux lamps.
http://www.yousendit.com/download/TEhXaklqaysxUUJjR01UQw?cid=tx-02002207340200000000&s=19102

Img 5 is a gross overexposure. Interestingly, ACR 7.1 renders the image as bright red on the screen. It looks white with Rawdigger.

http://www.yousendit.com/download/TEhXakl0NEhkMnMwTWRVag?cid=tx-02002207340200000000&s=19102

Readers can perform their own analysis, but here is my evaluation. I took two exposures with the metered reading, and the uploaded shot is exposure 1.

« Last Edit: August 22, 2012, 06:51:48 PM by bjanes » Logged
Graystar
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« Reply #77 on: August 22, 2012, 07:43:38 PM »
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Sorry, but I did not know what type of raw files you were seeking. I have uploaded files for calibration procedure to Usendit.

Thank you for those images.  They confirm what I've been saying.

Matrix metering tends to set exposure around 1/3 stop higher than Spot/CW metering (as an aside...I think the actual value is smaller, and depending on the camera settings Matrix is usually 1/3rd stop more exposure and occasionally it's the same as Spot/CW.  At least that's what I've found on my D90, and it would appear that the D800 is the same.)

As stated, the metered value is 15% of the max value.  But that's with Matrix metering.  If Spot metering had been used then the metered area would likely end up around 12%.  It's pretty obviously to me that the D800's metering and RAW levels are much like my D90 (don't see why it wouldn't be) and spot metering a 12.7% gray card will likely get any bright whites under the same lighting near saturation without clipping.
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bjanes
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« Reply #78 on: August 22, 2012, 08:09:39 PM »
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Thank you for those images.  They confirm what I've been saying.

Matrix metering tends to set exposure around 1/3 stop higher than Spot/CW metering (as an aside...I think the actual value is smaller, and depending on the camera settings Matrix is usually 1/3rd stop more exposure and occasionally it's the same as Spot/CW.  At least that's what I've found on my D90, and it would appear that the D800 is the same.)

As stated, the metered value is 15% of the max value.  But that's with Matrix metering.  If Spot metering had been used then the metered area would likely end up around 12%.  It's pretty obviously to me that the D800's metering and RAW levels are much like my D90 (don't see why it wouldn't be) and spot metering a 12.7% gray card will likely get any bright whites under the same lighting near saturation without clipping.

According to my own tests with the 800e, if one is using a uniform target which occupies the whole field of view, the reading are the same regardless of the metering mode. This is also what is stated on the Rawdigger site:

"the grey target (a grey patch can also be used, as well as plain white paper, without optical whiteners). Turn off all exposure adjustments and shoot. If the target takes up the entire field of view of the shot, then the setting of the exposure meter does not matter; all settings (spot, matrix, center-weighted) will result in the same exposure. "

According to that article, the exposure results can also vary with the ISO and also the illumination. The spectral sensitivity of the meter may differ from that of the sensor.

Regards,

Bill
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« Reply #79 on: August 22, 2012, 09:01:27 PM »
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Not for nothing but you all realize this thread is in the Beginners' Questions forum? Ya all might want to keep that in mind...perhaps a new thread not here would be in order. Pretty sure many/most readers of the thread have run away and hidden already.
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