The compromise, though, is that the Canon G3X's lens has a dimmer variable aperture, which drops from f/2.8 at wide angle to f/5.6 at full telephoto. 600mm equivalent (220mm), f/5.6, 1/500s ...

(From Pentax lens literature) The Pentax SMC P-FA 600mm f/4 ED IF telephoto is an ideal lens for professionals and advanced amateurs interested in sport and wildlife photography. It incorporates ...

"The SMC PENTAX-A 600mm f/5.6 ED (IF) lens meets professional standards by incorporating Extra-low Dispersion (ED) optical elements to produce a sharp, crisp image with minimal chromatic aberration.