I have the Nikkor 4.5/300 AI and the Nikkor 4/300 AF-S. The 4.5/300 is not bad, but the more modern / recent 4/300 AF-S is much better in all relevant parameters.
The Nikkor 4/300 AF-S
- can be used at open aperture without any problems, both sharpness and contrast are very good
- excellent performance at f5.6 (it is the "sweet spot" of this lens, with best overall performance)
- very even performance over the whole frame at all apertures
- very short closest focus distance of only 1.45 meters
- very fast and accurate AF
- very good manual focussing
- very good handling
- very good performance with the TC 14EII teleconverter
- I have often had very sharp shots even with only 1/125s when used with the F6 (the perfect mirror and shutter dampening of the F6 also plays a role here)
- as this lens has an aperture ring, it can also be used without limitations on older Nikon bodies.
Best regards,
Henning