I brought this lens winter of 2016 from a private seller who looked after it well, I had heard many good things about it but also a few regarding its apparent slow focus - well after having it for just over a month I can say that paired up with my D7100, I find its a fantastic combination and suite each other perfectly.
My previous long zoom lens was the AF-S 70-300 VR ED but I found the iq at 300mm a bit lacking even after stopping down - No sutch worries with the 300 f4 its sharp even wide open at a very respectful f4, and if you make use of the focus limiter switch(as I do) the focus is as fast as the 300VR zoom was.
Its heavy when compaired to a plastic bodied zoom but built like a tank with a all metal/all glass set up and feels well balanced on the D7100, Its very reasuring to use knowing how well built it is and in use its faultless and consistant.
Picture quality out of the lens is very punchy with great contrast, and a strange but very happy optical thing I have noticed - distant objects seem less affected by distortion and keep thier shape very well.
All in all its a Brilliant lens and well worth what I paid for it