Most wildlife photographers will say the same thing; I sure wish I had a bigger telephoto lens. It just seems you can’t get close enough to wildlife, especially birds. One way to extend the range of your telephoto lens is by adding a teleconverter. I have all the converters Nikon makes, but generally stick to the 1.4x because there is little loss of image quality. If I had to put a number on it, I would say around 10% image quality loss with the 1.4x, about 17% with the 1.7x, and around 20% with the 2x. I have no data to quantify this, just a gut feeling I get when I am working on my images using converters. But I have no hesitation using a 1.4x, especially if my subject is in the center. Center sharpness is very good, and the slight loss of acuity on the edges doesn’t really impact my images.
But then I wondered…I have been using the TC 1.4X II, the older version of this converter. The new version, the TC 1.4x III, was supposedly sharper. Really? So I bought the new version, and headed into the woods with my 600mm F4 with the new 1.4x attached, resulting in a 840mm F5.6. But before I even left the house, I set up my lens calibration target to fine tune the autofocus. I found a setting of -7 was about perfect…the images looked very sharp. Another point is worth mentioning. Starting with a fast tack sharp prime lens will obviously give you better results than using a converter on zoom lenses. That said I get excellent results using my 1.4x with my 70-200mm F2.8. Remember, you lose a stop of light using a 1.4x, so my F4 lens turned into a F5.6 lens. But autofocus was still fast and crisp in good light conditions.
I can tell you right now this new converter is sharper than the older version. Reviews have said the new TC 1.4x works better with lenses with electronic apertures (the E designation). My 600mm is an ‘E’ lens, so maybe that helped. But all I can say is these images were very sharp using my D5. Center point sharpness had just a tiny loss compared to using the 600mm with no converter. What really mattered was my camera technique. Shooting a 840mm lens requires lots of stability and fast shutter speeds. I never use VR on my 600mm, I just shoot it wide open and above 1/1000 as much as I can. Cree and I are big bird photographers, and have considered the 800mm 5.6 lens for years. But $16,000 is a lot, and you have less flexibility shooting at 800mm all the time. But of course this lens has legendary sharpness. I do like the flexibility of using my 600mm at F4, and then adding a converter if I need extra reach.
An interesting question is can you get better results interpolating (making your images bigger) in the computer or using a converter? Right now I would say using a 1.4x converter on a sharp prime lens is a better choice. But if you use a 1.7x and 2x, this might be more even in the final results. On a side note, as I was shooting this morning with my 600mm with 1.4x I found a very rare (in Colorado) golden winged warbler. I was giddy just standing there with my huge glass on my gimbal RRS tripod. The bird landed right in front of me, and I just blazed away with my D5….oh yeah!