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Author Topic: Canon 6D Under-Exposing?  (Read 12866 times)

Area256

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Canon 6D Under-Exposing?
« on: December 05, 2012, 12:21:53 PM »
This article suggests that the Canon 6D images are darker by about 1-2 stops vs. other Canon and Nikon cameras with identical settings (at least with long exposures).

http://www.borrowlenses.com/blog/2012/12/is-the-canon-6d-under-exposing/

I'm skeptical about this, and currently the article did the tests only with jpegs - so it's entirely possible this just has something to do with the jpeg engine or jpeg settings.

However, I was wondering if anyone who owns a 6D has seen this issue?  or can confirm this issue does/doesn't actually exist in the RAW files?
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Canon 6D Under-Exposing?
« on: December 05, 2012, 12:21:53 PM »

x-vision

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Re: Canon 6D Under-Exposing?
« Reply #1 on: December 05, 2012, 02:18:19 PM »
These shots confirm what I've noticed with other 6D test shots: that the 6D has a tendency to 'expose to the left'.
Reminds of my 40D, which does the exact same thing.

Not sure why Canon decided to implement the 6D exposure like that but I can tell for sure that this was their intent.
Overall, nothing to worry about. This is not a 'bug' but a feature ;).
« Last Edit: December 05, 2012, 02:23:58 PM by x-vision »

Tozz

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Re: Canon 6D Under-Exposing?
« Reply #2 on: December 05, 2012, 02:58:34 PM »

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Re: Canon 6D Under-Exposing?
« Reply #3 on: December 05, 2012, 03:27:51 PM »
Well, as somebody in the comments section of that page mentioned, if its underexposing, a long exposure (like the 30 seconds in the night shot of San Francisco on the link) will exacerbate the issue.

The test shots on those links were shot at 1/4 sec.

I am pretty concerned about this issue, I'm really hoping it's just the factory settings, like Auto Lighting Optimizer being turned on.

My T2i overexposes constantly, especially with my 28-135mm. I'd really like to be able to use aperture priority mode without having to mess with the EV settings constantly.

DanielW

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Re: Canon 6D Under-Exposing?
« Reply #4 on: December 05, 2012, 03:33:53 PM »
Well, as somebody in the comments section of that page mentioned, if its underexposing, a long exposure (like the 30 seconds in the night shot of San Francisco on the link) will exacerbate the issue.

The test shots on those links were shot at 1/4 sec.

I am pretty concerned about this issue, I'm really hoping it's just the factory settings, like Auto Lighting Optimizer being turned on.

My T2i overexposes constantly, especially with my 28-135mm. I'd really like to be able to use aperture priority mode without having to mess with the EV settings constantly.
I oftentimes shoot with my 60D overexposing by 0.3 stops (sometimes 0.6), and it has never annoyed me. I just set it to +0.3 and leave it like that.

Liverastic

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Re: Canon 6D Under-Exposing?
« Reply #5 on: December 05, 2012, 03:42:15 PM »
Well, as somebody in the comments section of that page mentioned, if its underexposing, a long exposure (like the 30 seconds in the night shot of San Francisco on the link) will exacerbate the issue.

The test shots on those links were shot at 1/4 sec.

I am pretty concerned about this issue, I'm really hoping it's just the factory settings, like Auto Lighting Optimizer being turned on.

My T2i overexposes constantly, especially with my 28-135mm. I'd really like to be able to use aperture priority mode without having to mess with the EV settings constantly.
I oftentimes shoot with my 60D overexposing by 0.3 stops (sometimes 0.6), and it has never annoyed me. I just set it to +0.3 and leave it like that.

Are you looking for a brighter look, or does +0.3 look more correct? I'm constantly moving between -.6 and -1.3 just so images aren't totally washed out and clipping.

Sorry if this is derailing the thread a bit. It seems like this could have a major impact on night sky/star field shooting, which I am looking forward to doing when I go full frame.

Area256

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Re: Canon 6D Under-Exposing?
« Reply #6 on: December 05, 2012, 03:57:14 PM »
So why is the difference between this 2 shots not that big??
http://img1.focus-numerique.com/focus/articles/1566/canon-6d-100iso-nrstan-big.jpg
http://img1.focus-numerique.com/focus/articles/1541/nikon-d600-100iso-nrstan-big.jpg

Both
ISO100, f/5.6, 1/4s

I'm guessing the Nikon is about 1/3 of a stop brighter here, but it's not a big deal, and it could just be caused by the transmittance of the lenses used - or any number of jpeg engine differences.  So for normal applications, I'd guess we won't see a meaningful difference.

However, I'm a little worried about long exposures.  Interestingly Canon seems to recommend ISO 400 for bulb exposures... I wounder if this is the reason for that?
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Re: Canon 6D Under-Exposing?
« Reply #6 on: December 05, 2012, 03:57:14 PM »

BruinBear

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Re: Canon 6D Under-Exposing?
« Reply #7 on: December 05, 2012, 04:13:37 PM »
So why is the difference between this 2 shots not that big??
http://img1.focus-numerique.com/focus/articles/1566/canon-6d-100iso-nrstan-big.jpg
http://img1.focus-numerique.com/focus/articles/1541/nikon-d600-100iso-nrstan-big.jpg

Both
ISO100, f/5.6, 1/4s

Could be differences in the lenses. Do you know what lenses were used for this test? D600 looks sharper but could just be the lens.
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DanielW

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Re: Canon 6D Under-Exposing?
« Reply #8 on: December 05, 2012, 04:18:38 PM »
Well, as somebody in the comments section of that page mentioned, if its underexposing, a long exposure (like the 30 seconds in the night shot of San Francisco on the link) will exacerbate the issue.

The test shots on those links were shot at 1/4 sec.

I am pretty concerned about this issue, I'm really hoping it's just the factory settings, like Auto Lighting Optimizer being turned on.

My T2i overexposes constantly, especially with my 28-135mm. I'd really like to be able to use aperture priority mode without having to mess with the EV settings constantly.
I oftentimes shoot with my 60D overexposing by 0.3 stops (sometimes 0.6), and it has never annoyed me. I just set it to +0.3 and leave it like that.

Are you looking for a brighter look, or does +0.3 look more correct? I'm constantly moving between -.6 and -1.3 just so images aren't totally washed out and clipping.

Sorry if this is derailing the thread a bit. It seems like this could have a major impact on night sky/star field shooting, which I am looking forward to doing when I go full frame.
I see no problem at all in derailing...
I've found myself quite often disagreeing with the camera's meter and increasing exposure in LR, and (although those with better knowledge on the subject may disagree) digital sensors deal better with overexposure than the opposite. I always shoot RAW, so I can bring exposure down if necessary with no loss of detail; on the other hand, I would probably introduce noise if I were to bring exposure back up.
It might sound like it's all good, but I've screwed up a few (too many) shots already by doing like that. When shooting something important, I always overshoot and vary exposure.
I think it's about knowing your camera, too, and having it do what you want and adapt it to your own photographic tastes/needs.
Neuro and others here sure know it in details; I just read it in one of the first books I bought (read quote below) and believed... :)

"The camera’s sensor does not give equal weight to all tones. In fact, your digital sensor is heavily weighted to the brightest areas in your photo. (...) Taken another way, the camera has a fixed number of numeric values for describing the brightness of a pixel. Fifty percent of those numeric values are devoted to the brightest f-stop in your photo. Each successively darker f-stop receives one-half the number of the f-stop ahead of it, until the shadows receive only a small sliver of the total possible values. This is important information, because all detail in your photos is a result of subtle differences in tone and color between adjacent pixels. In the shadows, where fewer values are available to describe these differences, it becomes more difficult to retain details. Underexposing photos drives more of the information contained within a photo deeper into the shadows, causing a loss of detail and an increase in noise (unwanted color impurities) in the photo."
(Taken from Perfect Digital Photography, 2nd edition, hopefully not infringing any copyrights.)

Hope it helps. :)
« Last Edit: December 05, 2012, 04:43:50 PM by DanielW »

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Re: Canon 6D Under-Exposing?
« Reply #9 on: December 05, 2012, 05:01:17 PM »
Not sure why Canon decided to implement the 6D exposure like that but I can tell for sure that this was their intent. Overall, nothing to worry about. This is not a 'bug' but a feature ;).

Indeed (if this is really the case) - on a consumer-oriented camera exposing to the left is the safe bet against blown highlights, esp. on a dr-limited sensor like Canon. People who shoot sooc jpegs and don't do much postprocessing probably will never notice the lower shadow resolution (esp. against ettr).

But no one stops you from using +1/3 ev exposure compensation all the time :-)

Artifex

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Re: Canon 6D Under-Exposing?
« Reply #10 on: December 05, 2012, 05:14:44 PM »
So why is the difference between this 2 shots not that big??
http://img1.focus-numerique.com/focus/articles/1566/canon-6d-100iso-nrstan-big.jpg
http://img1.focus-numerique.com/focus/articles/1541/nikon-d600-100iso-nrstan-big.jpg

Both
ISO100, f/5.6, 1/4s

Could be differences in the lenses. Do you know what lenses were used for this test? D600 looks sharper but could just be the lens.

I might be wrong, but I also think this could result as much of a lens difference than a camera difference. Even if both photo where taken at f/5.6, different lens have different light transmission for the same aperture; the light transmission is calculated by T-stop values, the F-stop values taking only in account the focal length divided by the diameter of the entrance pupil. There is normally not that much difference in light transmission between lens at the same aperture, but it could still be a factor.
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Re: Canon 6D Under-Exposing?
« Reply #11 on: December 05, 2012, 05:30:56 PM »
Well, as somebody in the comments section of that page mentioned, if its underexposing, a long exposure (like the 30 seconds in the night shot of San Francisco on the link) will exacerbate the issue.

The test shots on those links were shot at 1/4 sec.

I am pretty concerned about this issue, I'm really hoping it's just the factory settings, like Auto Lighting Optimizer being turned on.

My T2i overexposes constantly, especially with my 28-135mm. I'd really like to be able to use aperture priority mode without having to mess with the EV settings constantly.
I oftentimes shoot with my 60D overexposing by 0.3 stops (sometimes 0.6), and it has never annoyed me. I just set it to +0.3 and leave it like that.
I did the same with my 60D.. +.3 or +.5

Area256

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Re: Canon 6D Under-Exposing?
« Reply #12 on: December 05, 2012, 05:44:15 PM »
"The camera’s sensor does not give equal weight to all tones. In fact, your digital sensor is heavily weighted to the brightest areas in your photo. (...) Taken another way, the camera has a fixed number of numeric values for describing the brightness of a pixel. Fifty percent of those numeric values are devoted to the brightest f-stop in your photo. Each successively darker f-stop receives one-half the number of the f-stop ahead of it, until the shadows receive only a small sliver of the total possible values. This is important information, because all detail in your photos is a result of subtle differences in tone and color between adjacent pixels. In the shadows, where fewer values are available to describe these differences, it becomes more difficult to retain details. Underexposing photos drives more of the information contained within a photo deeper into the shadows, causing a loss of detail and an increase in noise (unwanted color impurities) in the photo."
(Taken from Perfect Digital Photography, 2nd edition, hopefully not infringing any copyrights.)

That is correct. If you want to know the reason is quite simple.  Humans see light in an approximately logarithmic fashion (as if we were taking the log (base ~2) of the actual light we see).  (We also hear in a logarithmic fashion as well.)  This is very useful to us since it means we can see when there are just a few photons, and when there are tens of thousands of times more photons per until area of our eyes - and yet it looks to us like it's only a few times brighter.

Sensors are linear, they just measure the approximate number of photons per pixel.  So if your images has 9 stops of dynamic range, the brightest stop has half the the available data.  And the darkest stop only has ~0.2-0.4% of the data.

Exposing to the right (as long as you aren't blowing out the highlights), is a very good idea if you want to have more freedom to play with your images afterwards - since you'll have much more data in the shadows.  Just one stop of "overexposing" will give you twice the shadow detail.

However I digress, and still want to know what's going on with those 6D long exposures...
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Re: Canon 6D Under-Exposing?
« Reply #12 on: December 05, 2012, 05:44:15 PM »

DanielW

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Re: Canon 6D Under-Exposing?
« Reply #13 on: December 05, 2012, 06:49:15 PM »
"The camera’s sensor does not give equal weight to all tones. In fact, your digital sensor is heavily weighted to the brightest areas in your photo. (...) Taken another way, the camera has a fixed number of numeric values for describing the brightness of a pixel. Fifty percent of those numeric values are devoted to the brightest f-stop in your photo. Each successively darker f-stop receives one-half the number of the f-stop ahead of it, until the shadows receive only a small sliver of the total possible values. This is important information, because all detail in your photos is a result of subtle differences in tone and color between adjacent pixels. In the shadows, where fewer values are available to describe these differences, it becomes more difficult to retain details. Underexposing photos drives more of the information contained within a photo deeper into the shadows, causing a loss of detail and an increase in noise (unwanted color impurities) in the photo."
(Taken from Perfect Digital Photography, 2nd edition, hopefully not infringing any copyrights.)

That is correct. If you want to know the reason is quite simple.  Humans see light in an approximately logarithmic fashion (as if we were taking the log (base ~2) of the actual light we see).  (We also hear in a logarithmic fashion as well.)  This is very useful to us since it means we can see when there are just a few photons, and when there are tens of thousands of times more photons per until area of our eyes - and yet it looks to us like it's only a few times brighter.

Sensors are linear, they just measure the approximate number of photons per pixel.  So if your images has 9 stops of dynamic range, the brightest stop has half the the available data.  And the darkest stop only has ~0.2-0.4% of the data.

Exposing to the right (as long as you aren't blowing out the highlights), is a very good idea if you want to have more freedom to play with your images afterwards - since you'll have much more data in the shadows.  Just one stop of "overexposing" will give you twice the shadow detail.

However I digress, and still want to know what's going on with those 6D long exposures...
Thanks for the explanation!
Are you familiar with some book or website where I can read more about it? I do enjoy digressions... :)

Martin

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Re: Canon 6D Under-Exposing?
« Reply #14 on: December 05, 2012, 07:31:29 PM »
The most funny and strange thing is that all Canons expose incorrectly and the most dissapointing thing is that almost no one in Canon would like to correct this (especially if we have to deal with banding when pushing up shadows) Some more advanced users noticed that especially when they has switched from Nikon or use any external light meter. To be honest it even does not require such a comparison. Just shoot any white wall or homogeneous surface. The histogram peak should be in the center. In canon bodies it is not. I've checked it with a lot of bodies and it always expose incorrectly. You even don't heve to mesure it-when you shoot any other brands-canons are darker. That's a huge mistake when you post process and its even more stupid if you shot jpgs.  I have no idea why people or other testing sites do not mention it loudly because it is serious and last for years. Take Nikon, take sekonic-identical metering, take Canon ca. -1/2 underexposure or even up to -1EV. As mentioned before I don't really get it, as Canon should have even a tendency to overexpose, cause there is a problem with banding when pp an underexposed image. Really strange for me...especially when we talk about a such a photo company.
« Last Edit: December 05, 2012, 07:33:45 PM by Martin »
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Re: Canon 6D Under-Exposing?
« Reply #14 on: December 05, 2012, 07:31:29 PM »