While the Canon 500mm F4 IS has been my bird-wildlife lens for years, I am soon purchasing a "pack canoe" that will allow me to go deeper into the backcountry. I may hike as far as a mile into remote ponds and wetlands for subjects such as moose, loons, otters, etc. Canoe, paddle, portage packs, and camera gear. No tripod. I need a lighter weight option other than the 500mm for subject in habitat type shots. While the perfect lens for this does not exist, I am struggling to find a decent option. My sold Canon 100-400 was the right idea and found nearby subjects shot to have excellent image quality, degraded quick when off in the distance.
The new Canon 70-300 L is perhaps a decent size and great for composing. Certainly short for loons other than those that dive next to my canoe! Moose if approached cautiously- perhaps good for habitat shots. No Canon teleconverter option. Wildlife most visible dawn and dusk so F5.6 not ideal.
Canon 70-200 F2.8 L II with a 2x III converter. Supposed superb image quality at 400mm F5.6 but heavier than desired.
Canon 400 F5.6 L. No matter how sharp and great people say it is for BIF, here in the northeast most subjects are photographed again in the low light of dawn and dusk. Not mid day light. Handholding this lens from a canoe without IS not a great option.
Canon 300mm F4 L IS. First generation IS. Great quality without converters starts to decline with the 1.4X but still decent? This seems to be my best choice.
Any advice or suggestions? In summary, 2 mile hikes, handheld from a canoe, low light AM and late afternoon. IS essential. Moose, loons, deer, otter, beaver. Given the lens szie limitation vs. a 500, talking subject in habitat shots vs. frame filling subjects. Visit my website and see the moose gallery to get the idea. I shot those with a handheld 500 but I was close to the road. Now I'm hiking back into remote places so the 500 will not work.