Prime lenses are sharper than zoom lenses because prime lenses don’t have extra glass inside that moves in order to zoom. This results, in better quality photographs due to less diffraction. Diffraction increases with the higher number of lens elements in zoom lenses.
Nikon teleconverters work best with Nikon’s prime lenses. Because the Nikon AI-S Nikkor 600mm F/4 ED-IF manual focus telephoto prime lens image is being enlarged, the effective lens aperture is decreased. Attaching a Nikon TC-300 2x teleconverter to the lens causes a aperture reduction from the native f/4 down to f/8. The lens requires more light and slower shutter speeds with an f/8 aperture. Aperture aside, the Nikon TC-300 2x teleconverter transforms the Nikon AI-S Nikkor 600mm F/4 ED-IF into a 1200mm telephoto lens.
The shallow depth of field bokeh that an f/4 aperture produces is lessened by the stopped down f/8 aperture. However, bokeh is also affected by compression. Compression pulls the background in closer. The Anhinga in this photograph was more than 100 yards away, but the wetland background was empty space for more than five times that distance. The 1200mm lens while focused on the subject compressed or pulled in the distant out of focus background and amplified the f/8 aperture’s bokeh effect.
- The stopped down f/8 aperture which is the bane of phase detect autofocus in low light, and Nikon’s stated minimum allowable aperture for autofocus to function is completely irrelevant with an old manual focus lens (heh, heh).
- The Nikon TC-300 2x teleconverter multiplies not only focal length but also any lens aberrations. However, Nikon’s superb AI-S Nikkor 600mm F/4 ED-IF build quality on my copy of this 38 year old prime lens mitigates the image degradation often sited with 2x teleconverters.
- F/8 aperture bokeh is often satisfactorily achieved with compression. The deeper depth of field of the f/8 aperture is often more desirable to render a sharp subject. However, the f/8 aperture requires more light. The fast shutter speeds often needed to freeze wildlife movement produce unacceptable high ISO graininess without good light.
- The image quality of often distant wildlife subjects is the point of this lens. This lens enables me to render photographs that would not otherwise be frugally possible. All lenses have limitations. Learning to work around those limitations is where the fun lies.