What is the influence of the camera on the performance of a lens?

Question

Shouldn't a lens be good or bad independently of the camera it is used with?

After seeing these reviews at DxOMark I got confused. By changing the camera where the lenses are tested I get different scores. I'm not talking about DX vs FX, because for sure something must differ from a full-frame to a cropped frame. But a score changing from a D5000 to a D7000 to a D90... why?

What is the influence of the camera on the image quality and performance of a lens?

Answer

A lens always performs the same way on all cameras with the right mount. What changes is the output from the camera which is dependent on both the lens and the camera.

Think of the light coming through the lens and then passing into the camera. The lens is first in the chain and always does the same thing.

Then, the light reaches the sensor which samples the light. A higher resolution sensor will be more demanding on a lens. There is also often an anti-alias filter in front of the sensor itself. This blurs the incoming light to avoid moire problems but that also means a stronger anti-alias filter will reduce the performance of top-quality lenses. For this reason, medium format systems (and Leica's own) do not use such filters.

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