Originally Posted by ntenny
I've great respect for the work done by C. Perez, but nevertheless I have to disagree concerning the statement that it is so seldom to get system resolution values of lens / film combinations delivering more than 100 lp/mm.
I have to disagree because of our own test results in our little non-profit optic test lab.
The bottleneck for getting high resolution is less the lens and film, it is
- absolutely precise focusing
- avoiding of all vibrations.
To get the optimum detail rendition the focus has to be absolutely spot on. You don't have any tolerance if you want best performance.
Therefore focus bracketing is needed in resolution tests. And Perez didn't use this technique.
If he had used it, his test results have been significantly better with higher values.
Focusing in medium format cameras with matte screen or split-image is not very accurate. You can try yourself: Make 15 shots of the same subject, each shot newly focused, and then compare all these shots at big enlargements.
You will see that you don't have 15 identically sharp shots, but several different sharpness and resolution levels. You probably even will have one or two almost unsharp shots, and most probably 2-3 really sharp shots with exact, precise focus.
Some test results from our test series (all with object contrast of 1:4, two stops):
Mamiya 645 pro TL with Sekor C 2,8/80 N at f5,6:
Provia 100F: 115 - 125 lp/mm
Agfa Copex Rapid: 130 - 145 lp/mm
Adox CMS 20 II: 195 - 210 lp/mm