SYS wrote in post #18552581
I know this is not a fair comparison, but the reason why I'm inquiring about this is because I sold my 100-400 and am thinking about getting Sigma 150-600 C.
Again, I know it's not a fair comparison, but for those with the experience with both lenses, how does Canon's IQ at 400mm compare to Sigma's IQ at 600mm given similar lighting situation and other conditions being equal? Does Sigma's IQ at 600 suffer noticeably in comparison? I intend to use Sigma more for bird "portraits" as opposed to BIF.
Sigma 150-600 all the way. There's no real appreciable difference in sharpness or anything. You're shooting portraits, the 600mm is going to give you more bang for your buck. Even if you were into BIF, both would be fine (for larger slower things). For zany close range BIF, I'd go with a prime for the edge in AF speed and aperture gains. But for just trying to get an excellent birding lens, the Sigma 150-600 is excellent, as is the Tamron. I'd get either over a Canon 100-400 for this purpose.
I use a 150-600 myself for the slow, big, or close range small bird portraits (song birds, lumbering osprey, etc).
For BIF, I use my 300 F4L IS and just apply a TC as needed, and I'm always very close to the subject (mostly fast shoreline birds like terns and smaller species).