[Klaus]

 Forgive me but could you accurately describe the use of "scaling"  and how you are applying it Klaus? although I have an idea of the principle a bit of clarity would be useful , I'm sure this could also help others too..........

 

Well, the ceiling of the chart is roughly defined by a "neutral" sharpening Imatest figure using a high end lens at an optimal setting. This approach is the same across all systems and invariant of the AA filter strength. The tuning factor is the base sharpening in the RAW converter. The idea is that the sharpening perception is the same on pixel level.

The bottom end is roughly defined as 1/3 of the ceiling but adjusted by a correction factor based on the sharpening used to achieve the mentioned neutral setting. From there on the scale is divided into the 5 segments representing the "school marks" or our version of the "subjective quality metric" if you like. 

 

This also means that technological progress on the sensor side is pushing all those values upwards making it more difficult for the lenses to achieve top marks. That is intentional. If the manufacturers release megapixel monsters, they have to push their lens quality as well in our opinion. 

 

Another way how to look at it:

On the 5Ds R the poor rating starts at a local lens resolution equivalent to the density of an 8 megapixel sensor.