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Author Topic: Shooting to the right  (Read 25135 times)
wynpotter
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« on: June 19, 2006, 09:33:36 AM »
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I have a CAnon 350d and if I shoot the meter bar at (0) then I seem to be underexposing. The histogram has about 1 stop more to the right
What is the general concensus on exposure  0,+.5, +1, ?
What seems to work best for you. Wyndham
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DarkPenguin
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« Reply #1 on: June 19, 2006, 09:44:27 AM »
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Anything from -2 to +2.  Depending on the situation.
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wynpotter
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« Reply #2 on: June 19, 2006, 09:52:48 AM »
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Another thought , are we calibrating our eye/brain to the image sensor?
Because it seem that each persons taste or perception of light would differ, but the sensor is a standard in the output, so to get the most pleasing image, we create our own subjective profile
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bjanes
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« Reply #3 on: June 19, 2006, 10:03:25 AM »
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Another thought , are we calibrating our eye/brain to the image sensor?
Because it seem that each persons taste or perception of light would differ, but the sensor is a standard in the output, so to get the most pleasing image, we create our own subjective profile
[a href=\"index.php?act=findpost&pid=68540\"][{POST_SNAPBACK}][/a]

I would submit that exposure to the right has little to do with percieved lightness or darkness of the image, but rather with maximizing image information and minimizing noise. A good start on understanding ETTR can be realized by reading Michael's essay on the subject on this site.

If the ETTR exposure looks too light as shot, then one uses negative exposure adjustment to get the proper balance.
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Anon E. Mouse
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« Reply #4 on: June 19, 2006, 10:40:28 AM »
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Finally, all images are subjective. The "exposing to the right" idea is just a rule of thumb (it used to be called "exposing for the highlights"). It ain't a hard an fast rule. It isn't a great way taken literally - the reasons camera metering does not use it. You may find the easiest "rule of thumb" is "expose for the subject." The imortant thing is your images look good.

In a sense, you are right that you need to learn to see how your camera sees. The human visual system plays a lot of tricks where your camera is very strict. Knowing how a scene will be reproduced by the camera is really important for determining exposures. There are no real rules for getting good exposures. The way the metering system works by using or averaging to a middle grey is about the closest thing to a "rule." But there are situations where that won't work. Experience is the best teacher.
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wynpotter
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« Reply #5 on: June 19, 2006, 10:49:47 AM »
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I agree that experience is the best teacher and the feedback from others down this path sure helps.Wyndham
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bruce fraser
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« Reply #6 on: June 19, 2006, 11:29:03 AM »
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Another thought , are we calibrating our eye/brain to the image sensor?
Because it seem that each persons taste or perception of light would differ, but the sensor is a standard in the output, so to get the most pleasing image, we create our own subjective profile
[a href=\"index.php?act=findpost&pid=68540\"][{POST_SNAPBACK}][/a]

There is a huge variation in the sensititivity of the sensors in just about any DSLR model line. Nominal ISO 100 can really be anything from about 70 to about 170. The camera meter doesn't know this.

You need to learn the behavior of your camera and not worry about what other people are doing with exposure, because their cameras are almost certainly different from yours.
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Gary Ferguson
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« Reply #7 on: June 19, 2006, 11:42:57 AM »
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There is a huge variation in the sensititivity of the sensors in just about any DSLR model line.


That's interesting, and something I've never heard stated so clearly. Could this explain why my Canon 1Ds often suffered from burn't out highlights, where as my 1Ds MkII hardly ever has this problem?
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Gordon Buck
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« Reply #8 on: June 19, 2006, 11:43:04 AM »
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Interesting to me is that, as I push exposure to the right, ACR tends to adjust oppositely; that is, underexposes.

I realize that this overexposure/underexposure is some sort of combination of my own particular camera, my own adjustments -- not to mention eyesight and small screen, and ACR auto exposure.  Nonetheless, it does happen.

Sometimes I just overdo the "push to the right" concept but I'm becoming better calibrated with practice.

Sometimes the "problem" is obviously in ACR; or rather, a difference of opinion between me and ACR as to how much clipping to permit in the highlights.
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wynpotter
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« Reply #9 on: June 19, 2006, 12:08:55 PM »
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There is a huge variation in the sensititivity of the sensors in just about any DSLR model line. Nominal ISO 100 can really be anything from about 70 to about 170. The camera meter doesn't know this.
[a href=\"index.php?act=findpost&pid=68552\"][{POST_SNAPBACK}][/a]

So this opens another possibility. I started this thread based on the idea that the sensor was a calibrated ref point and I was the subjective variation. How do we find out what the true (reasonably) iso scale is for a sensor. Gray scale card and external light meter compared to profiled monitor? This is a bit "Alice in Wonderland" but interesting.
Wyndham
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bruce fraser
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« Reply #10 on: June 19, 2006, 12:25:56 PM »
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That's interesting, and something I've never heard stated so clearly. Could this explain why my Canon 1Ds often suffered from burn't out highlights, where as my 1Ds MkII hardly ever has this problem?
[a href=\"index.php?act=findpost&pid=68553\"][{POST_SNAPBACK}][/a]

If you haven't taken steps to nail down, and compensate for, the systematic inaccuracies in the camera's metering system then yes, that's entirely possible.
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abaazov
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« Reply #11 on: June 19, 2006, 01:05:39 PM »
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bruce what are you referring to when you say to take steps to nail down and compensate for the systematic inaccuracies in your camera's metering system?

amnon
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bjanes
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« Reply #12 on: June 19, 2006, 01:08:59 PM »
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There is a huge variation in the sensititivity of the sensors in just about any DSLR model line. Nominal ISO 100 can really be anything from about 70 to about 170. The camera meter doesn't know this.

You need to learn the behavior of your camera and not worry about what other people are doing with exposure, because their cameras are almost certainly different from yours.
[{POST_SNAPBACK}][/a]

With more advanced models from Nikon and Canon, I doubt there is that much variation. The Nikon guru Thom Hogan states that there is a nearly 0.5EV tolerance in manufacturing standards, but he states that in his evaluation of literally dozens of Nikons, he rarely seen any significant deviation between bodies.

Nonetheless, it is advisable to check the meter and DPReview does this routinely. In the D200 test, they stated that the meter was right on as is usual with Nikon cameras. They noted that Canons tend to give about 0.3 EV more exposure.

An easy way to check the meter is to take a picutre of a gray card. With a gamma of 2.2 and bit depth of 8 bits, the observed pixel value in the file should be 114. (Actually, the reflectance of the card makes little difference)

[a href=\"http://www.normankoren.com/digital_cameras.html#ISOspeed]http://www.normankoren.com/digital_cameras.html#ISOspeed[/url]

For exposure to the right, most authorities recommend that the highlight should be placed close to saturation and you can test the exposure compensation from the indicated meter reading to accomplish this at the same time.
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dlashier
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« Reply #13 on: June 19, 2006, 01:37:04 PM »
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There is a huge variation in the sensititivity of the sensors in just about any DSLR model line. Nominal ISO 100 can really be anything from about 70 to about 170. The camera meter doesn't know this.

You need to learn the behavior of your camera and not worry about what other people are doing with exposure, because their cameras are almost certainly different from yours.
[a href=\"index.php?act=findpost&pid=68552\"][{POST_SNAPBACK}][/a]

I recall reports from people who had two identical bodies that metered up to a 1/2 stop different due to sloppiness in factory calibration. In the case of owning two bodies it may be worth sending them in to have them equalized, but for the typical user you just need to learn the behaviour of your's and adjust accordingly. Matrix mode will also be fooled by some situations and underexpose as when taking a picture of a large white object (eg house or boat). You need to recognize this and compensate, either with +EV or by metering to the side and recomposing. I just avoid the whole issue by metering manually. In the end it's easier and more consistent and predictible.

- DL
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John Sheehy
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« Reply #14 on: June 19, 2006, 01:48:20 PM »
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Another thought , are we calibrating our eye/brain to the image sensor?
Because it seem that each persons taste or perception of light would differ, but the sensor is a standard in the output, so to get the most pleasing image, we create our own subjective profile
[a href=\"index.php?act=findpost&pid=68540\"][{POST_SNAPBACK}][/a]

That is an outlook that really applies to JPEG more than RAW.  The JPEGs out of the camera have compression of the highlights, where they are not necessarily clipped but are pale and posterized, so exposing too far too the right, even if it doesn't result in clipping, can compromise the quality of the highest highlights.

For RAW, however, most cameras are linear or very close to it right up to clipping (if this isn't true for the lowest ISO, it is still true for the other ISOs).  You can't expose RAW too far to the right, except for clipping, and that occurs a bit higher than JPEG clipping.
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John Sheehy
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« Reply #15 on: June 19, 2006, 01:51:47 PM »
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There is a huge variation in the sensititivity of the sensors in just about any DSLR model line. Nominal ISO 100 can really be anything from about 70 to about 170. The camera meter doesn't know this.

You need to learn the behavior of your camera and not worry about what other people are doing with exposure, because their cameras are almost certainly different from yours.
[a href=\"index.php?act=findpost&pid=68552\"][{POST_SNAPBACK}][/a]

So, when are we going to get RAW RGB histograms in our cameras?  As a RAW shooter, I find the histograms on current cameras only slightly better than worthless.
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bruce fraser
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« Reply #16 on: June 19, 2006, 01:58:31 PM »
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With more advanced models from Nikon and Canon, I doubt there is that much variation. The Nikon guru Thom Hogan states that there is a nearly 0.5EV tolerance in manufacturing standards, but he states that in his evaluation of literally dozens of Nikons, he rarely seen any significant deviation between bodies.
[{POST_SNAPBACK}][/a]

I shoot Canons so I can't speak for Nikon, and the only people who have experience with statistically significant numbers of units are the vendors, who aren't saying. But Tom Knoll, who has had to shoot a lot of cameras to build ACR, has seen the same kind of variations I have. Jeff Schewe and I compared Canon 20Ds and 300Ds (3 of each) and found differences of about 2/3 of a stop. Greg Gorman had two IDs's that were about a half stop different.

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Nonetheless, it is advisable to check the meter and DPReview does this routinely. In the D200 test, they stated that the meter was right on as is usual with Nikon cameras. They noted that Canons tend to give about 0.3 EV more exposure.

An easy way to check the meter is to take a picutre of a gray card. With a gamma of 2.2 and bit depth of 8 bits, the observed pixel value in the file should be 114. (Actually, the reflectance of the card makes little difference)

[a href=\"http://www.normankoren.com/digital_cameras.html#ISOspeed]http://www.normankoren.com/digital_cameras.html#ISOspeed[/url]
[a href=\"index.php?act=findpost&pid=68564\"][{POST_SNAPBACK}][/a]

With all due respect to both you and Norman, a gray card isn't a terribly reliable method. On a linear capture, 18% reflectance is 18% of the way from black towards whiteit's awfully dark. You really need to meter the highlight, preferably with an external meter that lets you bracket ISO's. Then you can compare which ISO is actually closest to camera behavior.

Canons have more headroom than Nikons, but a good chunk of that "headroom" is driving the chip into the nonlinear range where the captured pixels may or may not be useful. That's a different phenomenon to the one under discussion.

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For exposure to the right, most authorities recommend that the highlight should be placed close to saturation and you can test the exposure compensation from the indicated meter reading to accomplish this at the same time.
[a href=\"index.php?act=findpost&pid=68564\"][{POST_SNAPBACK}][/a]
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John Sheehy
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« Reply #17 on: June 19, 2006, 02:10:00 PM »
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So this opens another possibility. I started this thread based on the idea that the sensor was a calibrated ref point and I was the subjective variation. How do we find out what the true (reasonably) iso scale is for a sensor. Gray scale card and external light meter compared to profiled monitor? This is a bit "Alice in Wonderland" but interesting.
Wyndham
[a href=\"index.php?act=findpost&pid=68559\"][{POST_SNAPBACK}][/a]

There isn't a lot out there to help people see what the camera is capturing; at least not with the typical software.  There are only 3 programs I am aware of that can show you the actual RAW capture; IRIS, ImagesPlus, and DCRAW with the right command line arguments.  Trying to surmise RAW exposure from the RAW converters of choice is really futile.

If you're dealing with matte subject in consistent lighting, you can generally expose a grey card for +1 EC, use those manual settings, and expose without clipping.  With my Canon 10D, I could meter for incident light with my Sekonic L-558 at ISO 32, and shoot the Gretag-Macbeth color checker with the meter settings with the camera set to ISO 100, and the white square would not clip in the RAW data.  I believe metering for ISO 25 just barely clipped the green channel.

It's scary when you consider that people could take important shots, going through all the trouble of accurately metering for ISO 100, and getting 3x the shadow noise possible metering for ISO 32.  Even ISO 200 metered for ISO 64 would have much less shadow noise.

A camera, set to an ISO, basically has two different ISO sensitivities; the ISO of average metered value, and the ISO of maximum unclipped white highlights.
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John Sheehy
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« Reply #18 on: June 19, 2006, 02:26:26 PM »
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Canons have more headroom than Nikons, but a good chunk of that "headroom" is driving the chip into the nonlinear range where the captured pixels may or may not be useful. That's a different phenomenon to the one under discussion.
[a href=\"index.php?act=findpost&pid=68573\"][{POST_SNAPBACK}][/a]

If true for a given camera, that would only apply to the lowest ISO.

My 20D has a non-linear RAW response in the very top of the highlights, only at ISO 100.

What would be RAW level 3550 at any other ISO, gets stretched up to 4095, and the stretch starts somewhere around 3000 (anything below about 3000 is the same at all ISOs).  This, however, is exactly the opposite of what you'd expect from sensor saturation; you'd expect a lack of response to further photons.  Canon seems to be intentionally boosting limited sensor highlights to give the illusion of full DR at ISO 100.  IMO, they should have just used a little more amplification so that the 4095 point would be just below saturation.  This non-linearity can easily cause a converter to get the WB of extreme highlights wrong.

I don't use ISO 100 for anything with important highlights.  200 is my target ISO, when lighting permits.
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bruce fraser
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« Reply #19 on: June 19, 2006, 02:47:34 PM »
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If true for a given camera, that would only apply to the lowest ISO.
[a href=\"index.php?act=findpost&pid=68576\"][{POST_SNAPBACK}][/a]

Good point.

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My 20D has a non-linear RAW response in the very top of the highlights, only at ISO 100.
[a href=\"index.php?act=findpost&pid=68576\"][{POST_SNAPBACK}][/a]

Mine too.

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What would be RAW level 3550 at any other ISO, gets stretched up to 4095, and the stretch starts somewhere around 3000 (anything below about 3000 is the same at all ISOs).  This, however, is exactly the opposite of what you'd expect from sensor saturation; you'd expect a lack of response to further photons.  Canon seems to be intentionally boosting limited sensor highlights to give the illusion of full DR at ISO 100.  IMO, they should have just used a little more amplification so that the 4095 point would be just below saturation.  This non-linearity can easily cause a converter to get the WB of extreme highlights wrong.

I don't use ISO 100 for anything with important highlights.  200 is my target ISO, when lighting permits.
[a href=\"index.php?act=findpost&pid=68576\"][{POST_SNAPBACK}][/a]

I use ISO 200 if the sun is in the frame, But I've found that for more reasonable DR subjects, If I spot-meter the highlights and dial in +2.3 stops, I rarely get badly-blown highlights at 100 ISO, and I get a fair bit less noise. Your mileage may vary in that you may need to dial in a different compensation depending on your camera's real ISO sensitivity.
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