If transmission really was the most important factor then the Sony should be out scoring the Nikon. The Sony equals or beats the Nikon in all the listed categories and has the lowest transmission of the three lenses.
Transmission on macro scale, not micro. In fact, probably not even measured transmission, but rather the specified max aperture. That's why the 50/1.8 lenses outscore the 500/4 lenses.
If you look at the test results they are measuring the combination of lens and body. Hard to do otherwise. Makes comparison between manufactures difficult and less than meaningful.
Yes, and sorry, but I think you are missing the point. For every measurement, all generated with a body attached, the Canon lens comes out on top, in some cases by a significant margin. Yet, the Score is a tie. So...the score is fabricated, pulled from their nether orifices, etc.
If you go over to photozone.de's page, they'll quite clearly state that the measurements (or scores) from one camera system (make + sensor size) cannot be compared with another. Given this I can't see why the same wouldn't be true for DxO. What does that mean? That you cannot compare a score of 25 for the Nikon lens with a score of 25 for the Canon or 22 for the Sony lens.
To be able to compare each lens properly would require each lens being mounted on the same camera.
How do they calculate their lens score? Would love to know but I'm pretty sure that it is corporate secret. For the Nikon one to be so high must mean that the readings are somehow weight on the sensor (e.g pixel size.)
The point is that they measure several parameters of optical image quality from the lens, such as sharpness, transmission, distortion, vignetting, and CA. They could
generate a Lens Score based on those parameters, but they don't. Had they done so, the Canon 500/4 II would have soundly trounced the Nikon 500/4.
For those who argue that it's reasonable that DxO consider the camera in the 'Lens Score', note that the sensor is already factored into the measurements themselves. P-Mpix measures sharpness of camera + lens, pixel size affects CA, etc. Even their transmission measurement changes with different cameras. So by factoring in the camera directly in the measurements (reasonable) then factoring it in again in the overall score where it's given an undisclosed (but evidently very significant) weighting, means their 'Lens Score' is as much if not more a camera score than a lens score.
One more point - considering just their P-Mpix measure of sharpness, by their definition the Nikon 500/4 results in a loss of more that 55% of the resolution of which the D800 sensor is capable, whereas the Canon 500/4 II only decreases the 5DIII's potential resolution by less than 14%. Of course, the Canon lens also outresolves the Nikon by an absolute assessment, even taking the higher resolution D800 sensor into account. But they get the same 'Lens Score'. Right.
They should rename their Overall Scores to a Camera Basic Score and a Lens Basic Score, so we could abbreviate them for what they really are: BS. Actually, that's probably giving them too much credit, because real Bovine Scat makes good fertilizer, whereas DxOMark's BS has no real-world utility.