I have the Canon 60D, which is a crop camera. I've recently purchased the Canon EF 24-105mm f/4L IS USM, which I'm now using as my walk-around lens instead of the EF-S 18-135mm f/3.5-5.6 IS kit lens. As I look at images that are in the common focal range between these two lenses, though, I'm not seeing any big improvements on the "L" glass shots I took on my most recent trip over photos from past trips when I was using the EF-S kit lens. I thought I'd be seeing better sharpness than I am. It's very possible it's a misperception on my part that the 28-105 f/4L isn't outperforming the old 16-135 f3.5-5.6. My expectations for getting my first piece of "L" glass may simply have been set too high. One of the things I've been thinking about doing, but haven't gotten around to yet, is setting up a series of tripod shots to shoot the exact same object with each lens at the same focal length and under the exact same conditions. That will give me the perfect way to truly comapre the relative performance of the two lenses. It's also possible that I'm just not experienced enough to be getting the best shots out of the lens. I'll be the first to admit that this is a distinct possibility. It has me wondering, though... is "better" glass always better for all cameras, or does an EF-S lens on a crop camera have some benefits over a nicer (aka more expensive) EF lens with a similar focal range? I understand the concept of the EF-S over the EF. A crop camera has a smaller sensor, so only a portion of what the lens is seeing is captured. The edges are "cropped" from the image that's saved. At a 1.6 crop factor, the 60D is losing about 38% of the image that a full frame camera would capture with the same lens at the same focal length. The EF-S lenses are designed to bring the glass closer to the sensor and better optimize the way the lens and the smaller sensor work together. The question is, how much optimization does the EF-S lens design have over an EF lens on a crop camera, and does this advantage possibly outweigh other factors such as the quality/speed of the glass? I see myself graduating to a full frame camera sometime in the future, so I won't be investing in any new EF-S lenses -- the 28-105 f/4L will most certainly be of use to me when I do, even if I prove to myself that I should go back to the EF-S lens on the 60D. That's the question. Which lens should I have on my camera now? Guess I need to go do some of those test shots this weekend.