Thanks for the comment, Wally.
I think the lens has a wonderful resolution, and my copy seems to be very well centered. It is considerably better than my copy of the AF 300mm/4 ED (non-AFS), and in particular wide open and close up, which was a pleasant surprise.
If set at it's minimum focus I can also get excellent results with my PN-11 extension tube, then only wide open due to the electronic aperture of the 300PF. General contrast at infinity seems to be about the same between these two lenses.
I was struggling a bit with the performance with TC-14E (I), however once I discovered some flaws in my tripod technique with D5100, it became clear that it resolves very well even then (much better than with the old AF 300/4) and most of the improvement occurs at only 1/3-2/3 stop down from wide open. Instead of the RT-1 i bought a Vello collar for it that is almost an exact copy at less than 1/3 of the price. It is quite well made made; if anything I could wish it to clamp a little tighter. I think it will be easy to modify it a little to do so if necessary. In spite of the short length and light weight of the 300PF one need to be careful with this lens, due to the low inertia on a light body. I found that trampling the ground 5m away from the tripod (Gitzo 120 w/BH40 head) was enough to cause a severe shake on a zoomed in live view screen. Shooting without mirror lockup in the critical range of 1/4 to 1/30 sec. or so did not give optimal results, and applying the equivalent of a "wine cork" between the lens and the mount does not improve results in this non-optimal situation so it does not look like the tripod mount is the weak point. (I did perform my first tests from live view but there was a too short exposure delay - all my 3 remotes broken...). Even combining TC-14E with the PN-11 for a 38mm wide field of view on a DX sensor gives very good results.
A very nice surprise was that autofocus seems to be right on with my D40x- IR720 body that has Lifepixel standard calibration (for the 18-70mm DX lens). With my old AF 300/4 i had to focus manually, and then do small visual defocus towards close range; I lost many captures over time when I forgot to do this.
As E-aperture is not supported on D40x (or my D200) the 300 PF can only be used wide open. Performance is so excellent that this is not a problem except when more depth of field is needed. Here are a couple of near visible infrared examples of long distance performance. The full frame is available for the first two if opened in a new tab. (As usual with IR captures, contrast was increased during post processing).
The Cold Climate Housing Research Center at University of Alaska Fairbanks.
#1
#2
The 300 PF can show some nice IR flares likely related to the PF element, under the right conditions when there is extreme overexposure of highlights:
#3
No problems with the high contrast in this IR capture though:
#4
