The lens offers an aperture range from f/4.0 to f/22. Amazingly I have utilized the f/22 aperture with good results when utilizing a teleconverter and an extension ring for maximum magnification and DOF. Of course contrast drops as does sharpness at f/22 but its still an outstanding performance even though I recommend avoiding anything over f13 unless the subject warrants such DOF.
Going on an African safari?
Overall, an outstanding performance at all apertures, especially at f/4. And remains just as sharp even when combined with a 1.4x converter. I close down only when I need more DOF or when I use a larger converter than my standard TC14E or stacked converters. A beautiful lens from the past that still has so much to offer.