Response to Enlarging lens resolution ?

I have checked the resolution of several top level enlarging lenses with a resolution transparency provided by Four Seasons, which is located in California, and advertises in Shutterbug. The Rodenstock f2.8, Schneider f2.8, Nikor f2.8 and Leica Focotar-2 f4.5 lenses all provide superb resolution, and my impression is that they are all diffraction limited from f5.6 to their minimum aperture. With the transparency I used the maximum guaranteed resolution is 160lp/mm, but the edges of the finer line arrays could be discerned clearly, and so it was possible for me to estimate a maximum resolution of 240 lp/mm. They all achieved this value at f4 to f4.5. The real difference is in color fringing and contrast. The Focotar won hands down in this department, and I think its reputation is based on this aspect of its performance. It also showed the best resolution across the field, and performed best at larger magnifications (10X and above). At f8 diffraction effects become evident if you observe the 12X magnified image of a negative with a grain magnifier under your enlarger as you stop the lens down. Contrast also suffers. It is ironic that this aperture is generally accepted as the best enlarging aperture. This is probabaly because all aberations and field curvature are overcome at this aperture, so that it is the best compromise. I believe that with the lenses mentioned above, that f5.6 is probably the best aperture. The bottom line is that these lenses will outresolve the detail in your negative, unless it is Tech Pan, and that they are not the weak link in the reproduction chain.

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