Roy C
Occasional bird snapper
I would not argue about the 100-400 as I have never used one (or any other zoom lens for birds as I have always preferred primes) but was only pointing out what loads of 100-400 users have said about the TDP comparison shots for this lens.I would have to respectfully disagree on your assessment of the canon 100-400 test being faulty, if you go to the comparisons and check out the Tamron 150-600 against the canon 400 mm prime, it compares quite favorably with that lens as well, the same can be done with all the canon lenses so to argue that the 100-400 is somehow not representative of accurate testing can not be justified.
There's not much in it when comparing the canon 400mm prime to the tamron at the same settings.
I have not got any long lenses for bird photography at the moment but as far as IQ goes when compared against a lens like the Canon 400/5.6 (which is both lighter and cheaper than the Tammy in the UK) I would say that the Canon, even when used with a 1.4x tc, is massively better in the corners and better in the mid frame than the Tammy, especially if you look at the fine vertical lines which would represent fine detail on a bird.
Maybe other folk see it different and it could be my old eyes playing trick on me :eek!:
Attached are the TDP compaisons for :
a) Canon 400/5.6 +1.4x tc v Tammy at 600mm - The Canon is wide open but both at f8 for comparison.
b) Canon 400/5.6 +2x tc (800mm) v Tammy at 600/f8
At the end of the day it does not matter a jot to me what lens folk use as long as they enjoy it.