We test the vignetting at infinity focus and using standard JPEGs (sometimes RAWs for cross-comparison) based on an evenly lit, back-illuminated test target. The displayed peak in the histogram (representing the gray value) is at the 3/4 position (we overexpose by 1-1.3 stops during the procedure). This approach is the same across all tested systems, of course.
So differences between the sites can occur due to
a. a different focus distance
b. a different exposure characteristic
c. a different S curve in the JPEG/RAW
d. a different tool used for the analysis of the test data
So differences between the sites can occur due to
a. a different focus distance
b. a different exposure characteristic
c. a different S curve in the JPEG/RAW
d. a different tool used for the analysis of the test data