A mid-range zoom on 35mm cameras that can substitute for a long zoom on a digital camera, the EF 28-135 IS USM was already a popular lens design. Its chief benefit is its Image Stabilization, which allows users to shoot handheld two to three stops lower than normal without significant motion blur Because its widest angle starts about 10mm into the telephoto range of the Digital Rebel's 18-55mm kit lens, the EF 28-135 is an excellent choice as an alternate lens that will complement rather than replace the kit lens. Its image stabilization helps offset the resulting blur potential from zooming out to the equivalent of 216mm. It's a good quality lens that comes in a bit cheaper than the EF-S 17-85mm that was designed to replace it. Test Notes This lens was a bit of a pleasant surprise when we tested it. One of us (Shawn) was quite familiar with it, as it had been a primary shooting lens for him for some years, first on film, and then on a Digital Rebel. As a result, we expected fairly positive results, but were nonetheless impressed by its sharpness at all but its maximum telephoto focal length/wide open, and by its relatively broad "sweet spot" one or two stops down. Chromatic aberration is moderate at the wide and tele end of its range, but quite low in between, vignetting is very low across the board, and Geometric distortion is on the low side of average. (About 0.6% barrel at maximum wide angle, dropping to about 0.2% pincushion at 60mm, and 0.3% pincushion at 135mm.) All in all, quite an impressive performance. While its 28mm maximum wide angle translates into an equivalent focal length of 45mm on the Rebel and 20D models, the 28-135mm IS makes for an excellent medium-long tele zoom, and the benefit of optical image stabilization is hard to overstate. If your photography tends more toward the tele end of the scale, this would make an excellent "second lens" as you add to your dSLR toolkit. Full-Frame Test Notes: As was the case when we tested it on the EOS-20D, the EF 28-135mm IS USM pleasantly surprised us when we tested it on the full-frame EOS-5D. It does get a little softer in the corners at wide angle with the larger sensor, and chromatic aberration , geometric distortion, and vignetting are all more pronounced, but for the money, it's a hard lens to beat. Sharpness and vignetting improve markedly when you stop down by one or two f-stops, to the point that even fairly fussy shooters would likely be satisfied. On the downside though, the lens' geometric distortion and chromatic aberration results betray its modest lineage. Barrel and pincushion distortion are on the high side at wide angle and telephoto focal lengths respectively, and chromatic aberration is rather high in the corners across the board (that is, regardless of aperture or focal length.) Still, this lens is an excellent value for the money, offering quite decent sharpness and IS at a bargain price. One thing that obviously changes as you move from sub-frame to full-frame is the angle of view of your lenses, and the 28-135's character changes quite markedly between sub-frame and full-frame bodies. On a camera like the 50/60D, this is a great lens for normal to mid-tele focal lengths, great for shooting amateur sports with. On the 5D though, its 135mm maximum focal length is only a relatively mild tele, not long enough for many sports shooting situations. Not that this is in any way a knock against the lens, it's simply a change that Shawn was particularly struck by when he first went out shooting with the 28-135/5D combination. He'd been quite familiar with the lens on his Digital Rebel, and grown accustomed to the focal length range it represented there. Moving to the 5D resulted in a very different visceral experience of the optic. We generally caution readers considering making the move to full-frame that it really brings with it a hidden commitment to excellent glass, because full-frame is so unforgiving of cheap optics in the corners. That said though, the 28-135mm f/3.5-5.6 IS amounts to a pleasant exception to the rule, as it's a lens that does surprisingly well with the larger sensor format. With its coverage from medium wide-angle to short/medium telephoto, it would make a great "starter" lens for someone looking to get into full-frame on a budget.