robertjerl wrote:
...the 100-400 zoom by Tamron it is much smaller and lighter (has an optional collar-use with a pistol grip or on mono/tripod)....
Poster appears to be looking for a non-interchangeable lens bridge or point-n-shoot with a super zoom... not a tele-zoom for their DSLR.
However...
Yes the 3rd party zooms are a little bit smaller (retracted into their storage position), but it's incorrect that the Tamron is significantly lighter weight....
Canon 400mm f/5.6L USM.... 2.75 lb. (includes tripod ring)
Canon 100-400mm "II" IS USM.... 3.5 lb. (incl. tripod ring)
Canon 100-400mm IS USM (orig. push/pull version)... 3.04 lb.
Tamron 100-400mm VC USD... 2.45 lb. (lens alone)... A035TM Tripod Ring... approx. .5 lb (estimated). Total wt.... 2.95 lb.
Sigma 100-400mm OS HSM... 2.75 lb. (no tripod ring provided , available or even possible)
So, any of these zoom options are the same weight or heavier than the Canon 400mm f/5.6L prime, assuming you want a tripod ring. At best you can save about 8 ounces over the Canon 100-400mm II.
The weight is the difference between metal (the Canon lenses, mostly) and plastic (the Sigma and Tamron)...
Or perhaps the difference between what Lensrentals.com called "the best-built zoom they'd ever seen" (the Canon 100-400 II) versus a more standard build...
Or between the Canon that's f4.5 to 135mm, f/5 to a little over 300mm and f/5.6 beyond that...
Versus a zoom that is f/5 only at it's very shortest focal length and drops to f/5.6 until 230mm, then is f/6.3 beyond that (the Sigma)...
Versus a zoom that's f/4.5 up to 135mm, f/5 to 180mm, f/5.6 to 280 and f/6.3 beyond that (the Tamron).
Of course, none of this is what the original poster is wanting.