« on: December 14, 2014, 05:05:54 PM »
+1A FF lens should outperform a crop lens when used on a crop camera.
Except when it doesn't. The EF-S 17-55/2.8 IS delivers better IQ than the 24-105L or 17-40L, plus it's a stop faster. The 17-55 beats the 16-35 II as well as having IS and being half the cost.
In the ultrawide to normal focal ranges, the smaller image circle makes optical design easier. That, in turn, leads to the potential for either lenses cheaper than 'comparable' EF lenses, or lenses similar in price but with better performance. As your examples highlight, in the telephoto range all that changes.
There are some lenses that Canon really got right when designing..... like the series 2 big whites.. but for zoom lenses you have to love the 70-200's for FF and the 17-55 for crops.... both examples of superb design that would be very hard to improve on.... and both are within the 3X zoom range limit. It is very hard to do a decent zoom with 4X or more zoom... too much compromise in the design...