[frank]

Hi Wim:



I can't resist to ask you a question on the optical resolution of a lens. Your replies seem to indicate that best lenses can reach 400-450 lp/mm at MFT-9. Is this resolution averaged over the whole image area?



The reason that I ask this question is that recently I tried to calculate the lens resolution at MTF-50 from the test result at photozone. The purpose was to see the difference between the lens resolution and the system resolution, and the influence of image sensor resolution on the system resolution. I know this is just a crude exercise but I want to get some feelings.



To my surprise, the center optical resolution can easily exeed 450 lp/mm even at MTF-50. Let me take the Nikon 16-35mm f4 lens as an example to show you how I calculated it. At 16mm and f4, the PZ test results on D3x are as follows:



center_res=3536 lw/ph, border_res=2700 lw/ph, corner_res=1278 lw/ph



which translate to lp/mm (divide above numbers by 2*24mm)



center_res=74 lp/mm, border_res=56 lp/mm, corner_res=27 lp/mm



These are system resolutions at MTF-50.



Now, the sensor resolution is 84 lp/mm (=4032/(2*24mm)). Then, using the formula



(1/system_res)=(1/lens_res)+(1/sensor_res)...........(a)



I get the optical resolution of the lens



ceneter_res= 599 lp/mm, border_res= 170 lp/mm, corner_res=39 lp/mm



So, even for a lens that is not the best, I get a center resolution about 600 lp/mm, at MTF-50. If this calculation is correct, the resolution at MTF-9 should be larger. Does my calculation make sense?



I know that for a real system there are more terms on the right-hand-side of equation (a), but those extra terms will lead to even larger optical resolution for a given system resolution (assuming those therms are positive).



I would like to hear your comments very much.



Best regards,

Frank