In my opinion, that is true. I have tried shooting a 100-400 with a 2X TC at a focal length at 800mm. The reading was 1/40 at f/11. But I had to manual focus the lens though. That is of course with IS. Hope this answers the IS question.
On the other hand if you are contemplating between the EF 75-300mm f/4-5.6 III USM and the IS version, this is what I have been told. The focusing on the IS version is dead slow because the IS version is the first lens to have the Image Stabilizing technology. It was really new and most likely that is why it caused this problem. There are 2 second hand ones sitting inside TCW. Go there and check it out for yourself.
it depends on what you are shooting, where u r shooting and wat is the corresponding ambient lighting conditions at that time.
IS is useful for pple who shoot under poor/low lighting conditions. ie, stage performance / shows where flash is not allowed. night shots, with low lighting.
IS only helps correct ur handshakes. hence, u r able to shoot at a lower shutter speed without worrying too much about handshake. sharp images shot at 1/15 or 1/30 can b easily taken when using Canon's 70-200 IS. BUT it does not freeze the motion of the subject like a flash. So that modern jazz dancer on the stage will still come out blur if u catch him/her in the middle of a spin.
if u r shooting in bright daylight where ur shutter speed in e ambient lighting is 1/125 or 1/200 and above, u dun need IS. in fact, if ur holding technique/ composition technique and experience is THERE, IS or no IS will not make a difference. flick the IS switch to OFF instead to conserve batteries. :think:
btw, i have a 75-300 III USM. but i have used 75-300 IS, 70-200 IS (thanks to agape01) and 28-135 IS. but i have yet to try the big mamas ... 400 IS, etc etc. ;p ;p
I was told having an IS makes little difference.. is that true ?