When I say same sensor area I mean when comparing:
Virtually the same... So how exactly is it that small pixels are better in low light? I remind you that you earlier said: "In practice, for moderate to high ISOs, smaller pixels do better."
How about "5D-III vs 1D-X" or "A7R vs D4"? (see attached)
Why is the red line above the orange line?
In practice, does pixel size affect low light performance for the same sensor area?
In practice, for moderate to high ISOs, smaller pixels do better.
Different sensors, entirely. The A7S has higher QE and lower read noise, neither of which goes with larger pixels.
Are those equal sensor technologies?
Virtually identical as you can see, plus DXO's testing doesn't for why smaller pixels win, which I posted up thread with samples.
In general smaller pixels appear to be ever-so-slightly-worse with SNR. If you consider the Dynamic Range you'll see that larger pixel are clearly superior at higher ISO. Colour sensitivity is virtually identical. I'm failing to see how smaller pixels (with equivalent technology) are any better in low light. In what way are they doing "better"?
As for your post on why smaller pixels win, how about this: 20MP, at 200mm f/4 which is sharper?
The image comparison there is flawed, as it is same-framing, rather than same subject distance. It doesn't matter what you do, if you put more pixels on subject, then your going to get a better result. The 6D has larger pixels AND more pixels, so when that test chart is framed identically, your putting more pixels, and more sensor area, onto the chart. Of course it is going to be better.
When you frame such that the subject fills the same absolute sensor area (in other words, the chart would have to fill only the central 1.6x crop area of the FF sensor that matches an APS-C sensor), then the smaller pixels are going to resolve more detail (all else equal...the 6D uses newer pixel technology, so all else is NOT equal.)
a) full-frame to full-frame
b) APS-C to APS-C
The 6D was released in September 2012, 7D-II has a newly developed sensor and was only just released in 2014. 7D-II also has been reported to have a higher QE than the 6D. Is it really fair to say that the 6D has newer pixel technology? Also, I just opened some CR2 files to look at the actual flie resolution. 6D resolution is 5472x3648 (19.96MP) and the 7D-II resolution is 5472x3648 (19.96MP). So in practical terms, no difference.
On my "flawed" normalizing:
1) Would you agree that a photographer should frame the subject as they intend to print it?
2) Should photographers use different composition rules when shooting on Full frame than they do when shooting APS-C? (i.e. Should Full frame users only frame their images in the tiny APS-C-equivalent portion of the frame?)
I didn't say it was your flawed normalizing, simply that the comparison itself was flawed, in the context of determining if one sensor resolves more than another, because the comparison was "same framing" rather than "same distance." Simple distinction, very important.
Regarding the 7D II, as far as I know the camera in discussion thus far was the 7D, not the 7D II. Still, it doesn't matter much. In a same-framing comparison, even if you have the same pixel count, the 6D is a full-frame sensor. Again, pixel size is irrelevant here...the larger sensor gathers more light. Period. More light, stronger signal, less noise. It's a very simple equation. Pixel size is immaterial to noise on an absolute-sensor-area basis in the grand scheme of things. Other factors about the pixels or sensor design, such as presence or strength of a CFA, the use or lack thereof of an AA filter, etc. can affect such comparisons...but when it boils down to pixel size and pixel size alone, it doesn't matter as far as noise goes. Bigger sensor, more light, stronger signal, less noise. That's all there is to it.
If you put more pixels onto a sensor, FF vs. FF or APS-C vs. APS-C, or FF vs. APS-C in a same-distance comparison, smaller pixels resolve more. Again, it's relatively simple. This should be obvious, of course smaller pixels resolve more. The key, when comparing FF to APS-C, is to make sure you've properly normalized. If you compare a full-frame camera to an APS-C camera in a same-framing context, then, relative to the scene, the pixels of the FF are smaller on a relative basis, thus they resolve more. Hence the reason it is important to compare FF and APS-C in a same-distance context. You could have fewer pixels on the APS-C, more pixels on the FF even, it doesn't matter. What matters is the total light gathered in your crop area. If the APS-C had larger pixels than the FF, and the FF was cropped to 1.6x size then downsampled, your STILL going to have the same noise...only the downsampled FF crop is going to be sharper.
Pixel Size <==> Resolving Power
Sensor Size <==> SNR/Noise
As for your two questions, they are irrelevant in the context of comparing two sensors on an objective basis. However, not everyone has the ability to always fill the frame with every sensor. Birding and wildlife are two great examples of reach-limited photography. You aren't always able to fully utilize the entire sensor surface with a FF sensor....sometimes you are FORCED to use only the central region (and possibly even less than a 1.6x crop equivalent area.) If you always have the ability to more tightly frame your subject, then the bigger the sensor, the lower the noise. Simple as that. If you are reach limited, then more resolution in a smaller sensor isn't going to hurt you over using a larger sensor with less resolution at the very least, and at best it would mean you have more detail with the same noise if you normalized (which, if your publishing to web, is pretty much always going to be the case.)
In a comparison of the 7D II vs. the 6D, which one wins? It entirely depends on what your shooting, and what your options are when shooting. The 6D will do better when you can utilize all it's pixels. The 7D II will do better when you are forced to shoot at a distance (and certainly when you need faster, more accurate AF.) The 7D II is packing the same pixel count into half the sensor area, so of course it's going to resolve more detail in a reach-limited situation. Conversely, of course the 6D is going to have less noise in a same-framing situation. If you had a 6D II with the same pixel size as the 7D II yet was still a full-frame and had an awesome AF system, then you would have the best of both worlds...resolving power, light gathering power, cropping power, sheer resolution.
This is pretty elementary stuff. I am always surprised that everyone has such a hard time with it. Not everyone shoots the same things, not everyone has unlimited budgets. Therefor, some people are always going to be able to fill the frame given what they shoot (portraits, weddings, street, studio, etc.), thereby maximizing the benefits of ever larger sensors. Concurrently, other people are always going to be reach-limited, always needing longer focal lengths and/or higher resolution sensors given what they shoot (birds, wildlife, landscapes, sports, etc.), thereby maximizing the benefits of ever smaller pixels. (Note, ever smaller pixels, damn the sensor size, it doesn't matter...you could have 7D II pixels in an APS-C or FF package...the reach-limited will always be able to use more resolution.) There will also always be some who want the best of every world, and those are the most demanding customers...wanting a balance of frame rate, AF performance, sensor size and pixel count. If it was possible to build a 15fps FF sensor with 80mp, someone would have done it, they would sell it for a mint, and they would have ecstatic customers from every walk of photographer life.