Quote Originally Posted by Claire Senft
If you use glass carriers and have a ten year old lens that is by one of the best makers you will find it to be diffraction limited at about f4. There may be higher contrast a f 5.6; However, any lens that reaches its best performance at f 6 can not out perform a lens that reaches its best performance at a wider aperture..this is not my opinion this is the laws of physics and light.
There are formulae to determine the threshold of diffraction that "limits" the resolving power of any given lens - but in this case I won't bother to wrestle with them. An enlarging lens for 35mm ... 50mm focal length or thereabouts - "diffraction limited" at f/4? I don't think so. Enlarging lenses follow the same "laws" as camera lenses .. there is only ONE "set" of laws. Camera lenses are normally equipped with iris diaphrams that only close to the "limit of acceptable diffraction"... typically, *any* 50mm (or so) lens will only stop down to f/16.... close to the limit of diffraction.

Why is it that so many are so critical of enlarging optics? A camera lens is designed around an "Optimal Aperture" but is certainly useable at a wide variety of others, and the same holds true for enlarging lenses.