Kudos to Canon for resisting temptation and not putting IS on a lens that doesn't really need it. Good job concentrating on improving the 24-70 in other, more important ways... and continuing to improve the high ISO capabilities of your cameras, which to a significant degree can offset the need for IS on any lens.
The 24-70/2.8 is targeted at relatively experienced users who are more likely concerned about other things... such as durability, sealing, premium image quality... than stabization on a focal length range where it's less necessary. It might have been necessary to compromise on some of the other important lens features, in order to include IS on it. I don't know... I'm not an optical engineer. I don't know if the above quote about negative effects of stabilization on wide and mid-range zooms is correct or not. I do know that that IS adds complexity and components to the optical forumla of any lenses it's implemented on. And some of those components have to move, too, to do it's job. That's more stuff inside the lens to wear out over time, or to require adjustment, or to break at the most inopportune moment. Not to mention, added cost.
Now with some lenses and for some users it's well worth the trade-offs to have IS. I'm a big fan of IS on telephotos and after using lenses with it for 10+ years, wouldn't want to be without it on my 200mm, 300mm and longer lenses. And, hey, if it's not an added cost, or I simply don't have a choice, I'll take it on any lens... It's generally reliable enough and worthwhile to have, rather than not have it. But, given a choice and all other things being equal, I wouldn't pay extra just to have IS on a 24-70 or a 16-35mm lens, especially if it also compromised the image quality!
Canon's selection of 70-200mm lenses gives us an opportunity to compare the differences necessary to add IS to a lens. In terms of cost, the 70-200/2.8 non-IS is about $500 less expensive than the original 70-200/2.8 IS, and fully $1000 cheaper than the Mark II version! The 70-200/4 non-IS is lists for nearly half the price of the 70-200/4 IS.
In terms of complexity...
70-200/4 non-IS is made up of 16 elements in 13 groups
70-200/4 IS uses 20 elements in 15 groups
70-200/2.8 non-IS has 18 elements in 15 groups
70-200/2.8 IS (original) uses 23 elements in 18 groups
70-200/2.8 IS Mark II uses 23 elements in 19 groups
Now, for me, the IS is worth some extra expense on a 70-200, 300mm and other longer focal lengths. I appreciate what it can do for me and would hate to not have it at available on those lenses. OTOH, it's a fairly low priority consideration for me on wider focal lengths. I can generally do without it on lenses less than about 100mm.
So then why did Canon - sort of out of the blue - launch 24mm and 28mm prime lenses with IS? My best guess... for videography. I don't see these lenses that cost double what lenses without IS in the same focal lengths (and a larger aperture in the case of the 28mm) as particularly appealing for still photoghraphy. But they might have some value for video. After all, that's where stabilization started and in use for many years before Canon began offering it on still camera lenses.
It's apples and oranges, comparing 24-70/2.8 with 24-105/4 IS... An f2.8 zoom is always harder to correct well, to design and manufacture to offer high image quality edge to edge. An f4 zoom can be more compact, is easier to extend to cover a wider range of focal lengths, and probably is easier to implement IS... it certainly makes more sense to offer IS on an f4 lens than an f2.8 lens.
JeffreyG wrote in post #14144665
What will be interesting will be to see how good the image performance of the new Tamron 24-70 with a stabilizer is.
A hint might be the 17-50/2.8 non-VR vs the more expensive, but noticeably less sharp 17-50/2.8 VR.
Maybe some day Canon will offer an IS version of the 24-70/2.8. If and when that happens, it will be interesting to see if people are willing to spend nearly $3000 for a standard zoom with IS, that likely will be bigger and heavier than "the brick" is today. Heck, it's going to be interesting enough to see if people will jump on the nearly $1000 more expensive Mark II! (List prices: Mark I $1400, Mark II $2300... and figure an additional $500-600 for IS). I suspect most of the people complaining about the lack of IS on this lens aren't likely to spend that kind of money on a standard zoom!