Still feel the images from the 300GM with 1.4TC are noticeably the best, color, contrast, acuity, detail, bokeh, it is a superb 420mm f4 lens. The bare lens will be just as great, but simply lacks the reach and magnification for bird photography.
These images were not shot with the 300GM, I used a rented 600GM for the trip. Then why would I post them you might ask
I'm going to make the annual trip to Bosque del Apache in November to photograph the bird migration and any other animals I run across. I loved shooting with the 600GM, size wise it wasn't that much of a burden.
This year, I was thinking about renting the 300GM with a 2x while taking along my 1.4x to see how well it performs. I think there was mention in this thread from a 600GM owner that it sees little use of the 600GM since the purchase of the 300GM.
Out of the group of owners and maybe this is a very small group, those of you who own the 600GM and are now shooting with the 300GM, would you leave the 600GM at home in favor of shooting with the 300GM and TCs? I'm also considering purchasing a 600 or 300 and I figured Bosque would be a fun place to put the 300 w/tcs to the test. Image quality/clarity/sharpness etc looks on point or really close to the 600GM from what I can tell based off of these shared images.
