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| p.8 #1 · Canon 24-70mm f/2.8L II tested by Roger Cicala |
Pixel Perfect wrote:
Why does everyone insist on acting like IS is like some lens add-on, rather than an optical element that has to be designed into the optical formula, and which can add some adverse effects or complicate the remainder of the design?
None of us know, including me, but it is certainly a possibility that Canon had the option of putting out an IS lens with good resolution or putting out a non IS with great resolution and chose the latter course.
This is the kind of decision lens design teams have to make every day - everything in optics involves trade-offs. It's just like the distortion at the wide end. It's easy enough to correct the optical formula for distortion, but the simple correction decreases resolution and can increase astigmatism. The designer decides which is most important for the purpose the lens is intended for.
I hate to find myself defending a camera manufacturer. It just doesn't feel natural. But sometimes it's not a plot.
Sounds logical until you ask why then the APS-C versions of the 24-70, all have IS? The Canon 17-55 f/2.8 IS is a stellar lens and having IS has not harmed it and the price while many complain is still only $1K. Sigma and Tamron have also done similar. Yet in the FF version on Tamron has pursued VC. Is the 24-70 VC a worse performer than the 28-75 and how could we prove VC was the cause even if it were?
Designing an APS-C circle covering lens is not the same as designing one for full frame.
The 24-70 VC is a reasonably sharp lens in some parts of the frame, but sharpness isn't the only measure of a lens quality.
I refute that IS has a detrimental effect on IQ, and most arguments for such degradation come from the poor old 300 f/4L IS not being as sharp as the non IS version. Maybe back then they didn't get it quite right, but I don't think it's the case now. All the superteles with IS were easily as sharp as their non IS predecessors and we only have to look at the 70-200 f/2.8L IS II to see the IQ vs IS argument evaporate.
Tele-photo lenses are not wide angle or normal lenses. What applies for one doesn't necessarily apply for the other. Tele-photo lenses require a different set of compromises and tradeoffs in their design.
I cannot work out Canon's logic as why would one need a 24/28 f/2.8 with IS, but not a 24-70 zoom. As for it pushing up the price, by that argument the 70-200 II should be $3.5K, yet is the same price give or take a $100 as the 24-70.
A prime is not a zoom and again has a different set of tradeoffs in lens design.
At the end of the day, none of us are lens designers and as far as I know no one on this board has ever designed one so in reality we're just speculating somewhat randomly and its all probably equally useless. I'd be curious to hear what an actual lens designer at Canon, Nikon, Zeiss, Leica, etc... would have to say about any o f these things.