The Pentax 300mm f/4 ED(IF) lens is a big improvement over the previous design. It is more compact and features Extra-Low Dispersion (ED) glass for improved optical performance, internal focusing for better balance, easier handling and considerably closer focusing capabilities.
Pentax lenses have been developed using the latest in computer-assisted optical design technology. Lens surfaces are treated with Pentax's exclusive Super-Multi-Coating for sharp, high-contrast images. ED(IF) lenses are super high performance lenses incorporating special Extra-low Dispersion (ED) lens elements to assure the highest image quality and minimize chromatic aberrations. The Inner Focus (IF) mechanism minimizes lens extension when focusing, maintaining good balance and assuring smoother focus ring operation and a closer minimum focus distance.