What is a HEAVY lens?

While reading reviews, I noticed many a folk complain about the weight of lenses. This is important, as less weight will keep you going longer... but when is too much and how much is too much?

Canon EF 24-70 f/2.8L - 950 grams (33.6 oz)

Canon EF 50mm f/1.4 USM - 290 grams (10.2 oz)

Canon EF-S 10-22mm - 385 grams (13.6 oz)

Canon EF 24mm f/1.4L ii - 650 grams (22.9 oz)

Canon EF 28mm f/1.8 - 310 grams (10.9 oz)

Canon EF 70-200 f/4L IS - 760 grams (26.8 oz)