lens - Upgrade from EF-S 15-85 IS

I currently own a Canon 60D, and I am perfectly happy with the camera. It is going to be years until I move to a better (most likely full-frame) body.

My main, walk-around lens is the 15-85. I am also very happy with this lens, although I also know its shortcomings, like the variable aperture (3.5-5.6).

But this morning, as a "what if" exercise, I started thinking about upgrading this lens.

Since my 60D is a crop sensor body, the closest and cheapest upgrade I can do is the 17-55 EF-S USM IS. It has a constant aperture of 2.8, and people say that it produces the best picture quality of all EF-S lenses. The upgrade would probably cost me $300-$500, depending on the price I sell my 15-85 at, and whether I want a used or new 17-55.

But 'upgrading' from an EF-S lens to another EF-S lens is not really upgrading, is it? It is more like switching between two similar quality products. Is it worth it?

A TRUE upgrade would be to get an L lens. So, assuming that price is no object (one can only dream :(), what L lens would you recommend to replace my 15-85?

EDIT: What I would look for in the ideal replacement lens.

Thanks for all the answers so far. One conclusion I came to after reading them is that there is no point for me to invest in L glass if I care about wide angle on my crop sensor body. And I do.

I like my 15-85 because it offers me the flexibility of being able to capture moments like a few snapshots in a restaurant with friends, or my 2 years old daughter who won't sit in one place for long - definitely not long enough for me to switch lenses.

I could give up the 2mm difference on the wide end of the spectrum, if the 17-55 offered me much higher IQ than the 15-85 does.

Hence the followup question - Please let me know if you upgraded from 15-85 to 17-55 and if that was a right decision.. I know it is all personal - and that is what I am asking about - what was your experience with such upgrade if you did it?

Answer

The EF-S 17-55 f/2.8 isn't an "L" lens -- that's absolutely true. Before dismissing it, though, I think it's important to remember that Canon won't label any EF-S lens an "L" since it wouldn't work on their pro bodies. The performance of the lens, though, is considered to be excellent -- definitely competitive with "L" offerings, and very possibly even better than something like the 17-40 f/4 L, which is highly-regarded on full-frame bodies, but isn't universally loved on crop-sensor bodies. In this instance, the EF-S lens only has to serve one master, which seems to give it a bit of an advantage.

The 17-55 can't offer a couple of benefits that are reserved only for "real" L lenses -- the red ring on the lens and "real" weather sealing. The red ring is cosmetic, of course, but if that sort of thing's important to you, you'd have to paint on your own ring if you got the 17-55. Weather sealing is another matter, though. Canon's pretty wishy-washy in terms of claiming weather sealing capabilities for anything short of its pro bodies and L lenses, but the 17-55 will be better than entry-level, even if it's not up to L standards.

Since you mentioned a possible full-frame upgrade at some point, that might also be a factor for you. You wouldn't be able to use any EF-S lens with a full-frame body, but quality glass tends to hold its value very well, which mitigates this inconvenience a bit.

While you're considering options, don't forget that you'd be giving up some zoom range moving to the 17-55. That may or may not be important to you, but the zoom range of the 15-85 is one of the things I love about that lens.

Lens purchases are always incredibly individualized decisions, and there's no single right answer for everyone when it comes to choosing a lens. The factors that make a lens right for you include your intended usage and the body you'll use for it, as well. When looking at wide-angle lenses on crop bodies, don't rule out an EF-S lens just because it's not an L.