Imatest resolution question - lens testing

[JR]

This may seem like a stupid question!  When we go on www.photozone.de to look at lens test and then compare resolution charts for each lens that are based on the Imatest (LW/PH), it make sense if I only look at Canon lens say done with a FF camera.

Where I am puzzle is why when I also look at the same test for a similar Nikon lens also done on a full frame camera the LW/PH and hence the resolution always seem higher (the graphs always show a higher number).  I thought that with the 5D at 21MP and Nikon FF being at 12MP these test would almost always show Canon lens having higher resolution.

Does anyone understand the differences?  Am I comparing apple to oranges here?  Thanks in advance for your response...

[ferdi]

As the Photozone team explains in their FAQ, the LW/PH value is hard to compare across systems:
http://photozone.de/Reviews/lens-test-faq

LW/PH [...] [is] basically a unit for resolution (not sharpness which is a combination of contrast and resolution) limited by the max. resolution of the camera's image sensor. You shouldn't take the LW/PH value itself too seriously because it is dependent on a number of factors. The analyzing tool (Imatest) is quite vulnerable to the quality of the source material.
[...]
In the future we will probably drop the LW/PHs in favor of a school mark system which is easier to read. Refer to the reference scale on the left of the MTF charts to classify the quality.

So just look at the good/very good/ex rating.

[J. McCabe]

This may seem like a stupid question!  When we go on www.photozone.de to look at lens test and then compare resolution charts for each lens that are based on the Imatest (LW/PH), it make sense if I only look at Canon lens say done with a FF camera.

Where I am puzzle is why when I also look at the same test for a similar Nikon lens also done on a full frame camera the LW/PH and hence the resolution always seem higher (the graphs always show a higher number).  I thought that with the 5D at 21MP and Nikon FF being at 12MP these test would almost always show Canon lens having higher resolution.

Does anyone understand the differences?  Am I comparing apple to oranges here?  Thanks in advance for your response...

Possibly the tests were done on the Nikon D3X, which has a 24MP sensor ?

[JR]

Oops!  You are right most of them are done with the D3x which has 24MP so that would explain it I guess.  I also understand I should not compare like for like different system but was just curious.

Thanks for pointing that out...