I just returned from a trip to Yosemite with ANPW, and conditions were unlike anything I’ve seen. With a snowpack approaching 200 percent of normal, and hot sunny conditions in the Sierras, the Merced river was flooding the valley floor. While this prevented us from shooting in some popular spots, the flooding created beautiful reflection pools in places I’ve never seen before.
One thing I wanted to try out was shooting my 300 PF F4 lens with my 1.7x converter. This 300mm F4 is one of my sharpest lenses, and being incredibly compact (about the size of a 24-70mm F2.8), I bring it with me on most of my travels. I have shot this lens with my 1.4x, making my 300mm a 420mm. Many photographers say you lose about 10 percent sharpness using this converter, but honestly this doesn’t affect my images that much. With the 1.7x attached to my 300mm I have a 510mm. Lens testers claim about a 20 percent loss of image sharpness with this converter. Once again I really didn’t see much of a sharpness issue (using my D810). Maybe if I took a really close look at the corners I can see find some loss of sharpness. The climbing image at top was taken with this combo. Autofocus with the 1.7x attached works fine in daylight, but may struggle a little in low light conditions.
If I attach the 1.7x with 300mm on my D500 (with 1.5x sensor), then my final angle of view is 765mm…in a small, compact system that has VR and can shoot at 10FPS. Incredible! The bottom line with the 1.7x for me is with a prime like the 300mm F4, there is very little image degradation. If I add this converter, or any coverer, to a zoom (with more lens elements), then the quality won’t be as good. But give converters a try. They give you a lightweight option for long lens shooting without carrying the big glass.