Quote Originally Posted by Yves
Nice to have would be a 70-300mm f/2.8L IS USM....That would be really ... big jump in...Size and Weight.

Such a lens, if made, would be significantly larger and heavier than either the 70-200mm f/2.8L IS II and the 100-400mm f/4.5-5.6L - probably at least twice the weight. With the same aperture, a zoom lens is always bigger a prime of the focal length at the long end of the zoom. So, the lens you think would be interesting, a70-300mm f/2.8L, would be larger and heavier than the 300mm f/2.8L prime - and even Canon's forthcoming newer, lighter version of that lens is 10" long and weighs over 5 pounds. Interesting, yes, but perhaps not in a good way...


Quote Originally Posted by Yves
If You have a 70-200mm f/2.8L IS II USM, do You want to buy a lens for 200-300mm with an aperture of f/5-5.6? And if You have a 100-400mm f/4.5-5.6L IS USM, do You want to buy a lens for 70-100mm, additional a little bit better max apertures from 100-230mm?

My answer is yes. In both cases, the reason to buy the 70-300mm lens is not primarily the extra 100mm on the long end (traded for aperture), or the extra 30mm on the wide end (traded for 100mm on the long end). Rather, it's the reduction in size and weight. I can tell you from experience - I have both the70-200mm f/2.8L IS II and the100-400mm f/4.5-5.6L IS - and sometimes carrying one of those lenses just is not practical. That's why I got the70-300mm f/4.5-5.6 DO IS lens, to carry when bringing one of the larger lenses won't work, but I don't want to give up a telezoom. If you want portable, you need to give something up. In the case of the DO, I am trading IQ focal length or aperture for portability. The option to trade only one - focal length vs. the 100-400mm or aperture vs. the 70-200mm II - and not sacrifice IQ, is what makes the new 70-300mm appealing.