I'm really surprised that Canon didn't manage to make the IS just as good. They had 6 years of experience and newer technology, and the IS surely only requires one additional lens element (or articulation of an existing element). Reader reviews at FredMiranda.com seem to concur with your reply, but it just doesn't make sense to me that the later lens has poorer IQ.
the problem with non IS is that you spend too much time wondering if that missed shot would have been saved with an IS lens ...
I had a non IS from new and the sold it after around 2 years for new IS version...
LOL. Considering the price difference I'll have to wonder a couple of years myself!
... the very sharp EF-S 55-250mm, with 4-stops IS, for £220? Or EF 70-300mm IS for £430?
I wouldn't do without IS, but you have to need f/2.8 really badly to go for that.
When I first started photography I thought of IS as quite a big deal, but I'm now tending to admire fast glass instead - as a
huge generalisation, on some occasions either IS or a wide aperture will equally "save the shot", on other occasions only fast glass will do it. I'm tending to think there are few occasions where IS will get a shot that a fast lens won't.
Both the EF 70-300mm IS & the EF-S 55-250mm are f/4 - f/5.6. For me the extra range, price & excellent quality of the EF 70-300mm IS would (and did) win over the EF 70-200mm f/4 non-IS, but shootin' bunnies, I don't believe that is fast enough. I've still got the EF 70-300mm IS, but I'd really love an EF 70-200mm f/2.8.
I have one landscape-y shot in particular here that was indeed saved by IS (and resting on a good surface). I don't know if it could have been any better, but I still wish I had gotten the tripod out the boot of the car & used it, instead. I was an inexperienced photographer at the time (and still am) but I want to be the kind of photographer who is disciplined enough to use a tripod whenever there's doubt. You can be more sure of a tripod than you can be of IS.
I think there's a tendency to think of image-stabilisation technology as a silver bullet. Sure, you can get the EF-S 18-55mm IS for £130, so you probably wouldn't pay £100 or even £80 for the non-IS version (assuming it was still available new at those sorts of prices), but there's a reason that fast glass still sells at these higher prices.
There is more to the 2.8IS than just the IS system, it is also weather sealed wheras the none IS is not.
I've learned something today - I had assumed all L lenses were weather sealed to the highest standards.
Stroller.