That "
you can see every feather barb at 100% view" argument only impresses
other photographers, Jon - it's essentially an irrelevance to anyone who views your images who
isn't a photographer.
(That said, I've supplied exactly the same sort of example myself to indicate the capabilities of the Siggy 120-300mm f/2.8 OS + 2x TC - I get the basis for doing so. But as I say, it's only interesting to photographers).
Steve's right on point here: nobody (least of all me) is trying to suggest that - other things being equal - the "best" kit won't serve to maximise opportunities, but for the most part it won't make an
appreciable difference in most circumstances: as we'd all acknowledge, there's more to wildlife photography than the gear.
Indeed, for my style of photography, an anchor of a lens - and tripod, and gimbal - would be a positive disadvantage: I like to be mobile, and I shoot exclusively handheld, not least because of the flexibility and "agility" this approach affords. A Canon supertele would positively slow me down. Even aside from the logistics of using such gear, the weight doesn't appeal either.
And here's another thing. I could have chosen a Canon 300mm f/2.8 IS instead of the the Siggy, but I have never, ever understood how any wildlife 'tog can function with fixed focal length lenses: I know they do, but it is a source of constant bafflement to me.
Even in the pics I've posted up here in the last day or two, the focal length is
all over the place - I literally could not manage without being able to zoom.
The only Canon "super" lens that gives something like the flexibility I need, is the 200-400mm f/4: I love the idea of that lens (especially with the built-in 1.4x TC), but - having seen innumerable examples from it - I'm back to "it's not
so much better in terms of the end result that I could justify it".
For the record, I have actually used a 600mm f/4 (not the latest version) at some length, courtesy of a UK pro shooter I'm friendly with, and - honestly - it's not for me. The disadvantages
to me that result from it aren't outweighed by the fairly minimal (at the image level) superiority of the lens over my kit.
Yes, it's sharper at 100%, and yes, it's AF is better than the Siggy + 2x. But my Siggy is much better at say, 300mm, and at f/2.8: and is at least as fast focusing as the 600mm when the Siggy is naked or with the Canon 1.4x attached.
I can't get out to 840mm/1200mm of course, but I've rarely if ever needed to, whereas I routinely need less than 600mm...
And I reiterate that
at the image level the benefits of the Canon superteles are largely lost on the viewing public: I have
never, ever been told that my efforts would be better
if only they were sharper...
As long as I can do
this at 600mm - and I can, all day long - I'm happy enough. And let's be honest: if I'd told you that it had been taken with a Canon supertele, you'd have no reason, on the basis of its sharpness and detail, not to believe me.
(It's almost wide-open, too - no drastic stopping down to get this level of sharpness).