Originally Posted by Goldwinger
PS. this is more of a question than an argument concerning weight.
The info I have is the Sigma weighs, 1390g (49.0 oz) and the Tamron,1330g (46.9 oz)
That's just 2.1 oz difference. is that enough to make a notable difference when hand holding?
It's been a while since I looked into these, but when they were first announced, (and even now on B&H's site) they list the Tamron at 1150g (2.5 lb) and the Sigma at 1370g (3 lbs). Looking on the Tamron site, the SP 70-200 is listed at 1150g but it's noted that this is without the tripod mount. My Sigma EX 300/2.8's short platform tripod ring weighs 138g (4.9 oz), and also fits the 70-200, so assuming the Tamron's is comparable, that would bring the weight difference down to something like 3 oz, so your figures are probably more correct, and this will minimize the difference in handling. Originally, I assumed the weight differential was largely due to the HSM motor, so I just accepted the figures.
Experience dictates that I don't believe published lens weight specs -- my FA* 300/2.8 is listed by Pentax at 2495g (@ 5.5 lbs), but with the standard protective front filter, the internal rear filter, and the hood, it actually tips the scales at 6 lbs 10 oz -- that's why I wrote that if weight is important, the OP should contact the mfgs to get real directly comparable weight specs.
I'm not really too weight sensitive for my birding setup since I'm usually tripod mounting the big glass, but after a few hours of constantly lifting the K20, 50-135, and the AF540 at my 40th HS reunion a while back, I was really getting shaky -- luckily the flash made this shake irrelevant, but the arm and shoulder fatigue and the elbow problems that I experienced after that made me much more conscious of weight in an event-type setting, and the Tokina 80-200 no longer is seen by me as a viable possibility for use as a candids lens. This getting old stuff is. . . well. . . getting old
Calling the weight thing even, I'd still choose the Tamron -- there'd just be one less reason. -- but that's just my very subjective perspective.