I have both lenses and have been very happy with both. On semi-static subjects like Bison, Big Horn Sheep and Coyote, I find the 400-800 to be great as well as bird on stick. I have a very limited number of outings with the 400-800 for BIF, but my results seem strange. While shooting on an A1 II, it seems like the 400-800 at 800 finds the birds faster and maybe holds better than the 300 GM with a 2X TC on it. But when I look at cropped images, the images from the 300 GM with 2X look much better.
Is this just an outlier based on limited attempts with variable lighting conditions and therefore ISO?
For shooters who do a lot of BIF and use both lenses, do you agree that the 400-800 seems to focus a bit faster and hold better than the 300/2X? Do you get better images from the 400-800 or does the 300 GM with 2X still outperform it despite only being at 600mm and lagging a bit in AF speed?
I have very limited data to work from. I don't do a lot of BIF in summer, but happened to be doing some on Bobolinks this summer. I would like to sort out what to take for a fall/winter trip. I have seen lots of reference in the 100-400 f4.5 GM talking about the AF speed of the 300GM with 2X TC vs 100-400 with 1.4X, but not much comparing the speed accuracy to the 400-800
Let me give all the caveats so I don't get called a moron!!
Shot on different days. Small birds with huge crops. It is a protected breeding area so you can't leave established trails to get closer. I know the "other factors' are likely to be as big as or bigger than the lens differences, but that is why I am asking the question.
Different shooting conditions and different methods of processing, I would say. It seems that the posted images taken with the 300mm plus TC are larger crops and a tad oversharpened relative to the others.
Thank you very much for sharing your images. I think they are overall beautiful, it is hard to get small birds in flight in general. I like the wing poses.
The 400-800 images are ISO12800 with the subject relatively small in the frame at even 800mm. I think you should give it another chance in better conditions.
Of course it would be valid to say that you were at ISO 12800 because of the f8 limitation of the lens, but that is another consideration.
