Performance and image quality
In our testing, we found the lens displayed minimal distortion across its entire range, which is excellent for its price class. There's only barely noticeable barrel distortion (where objects appear to curve toward the outside of the image) at 55mm and slight pincushion (where objects appear to curve toward the center of the image) at 135mm and 250mm. The lens exhibits excellent sharpness at 55mm in our lab tests, and slightly less sharpness at 135mm but still very good. However, fully zoomed out to 250mm the sharpness dropped off to just acceptable. While zooming, the lens maintains its maximum aperture of f4 from 55mm to 85mm, at 100mm it narrows to f5, and turns to f5.6 at about 140mm.
Hands-on
Mounted on our Canon Rebel XSi, the lens felt very light given its range, so it was no problem to carry for a day of shooting. The zoom ring is nice and wide, with a quick, fairly well-damped action. There's no lens creep, the unintentional movement of the zoom caused by gravity. The manual focus ring is located at the front of the lens and is very usable and yields a decent amount of control, but it's fairly noisy. We wouldn't buy this lens solely for manual focus; it will work fine when the need arises but doesn't seem to be intended for frequent use. The lens lacks a focus distance scale, although that's common for entry-level lenses. Its front-focusing design, where the front element rotates during focus, should only be an issue with circular polarizing filters. Although some might be tempted, this lens' slow maximum aperture range of f4-5.6 makes it a poor choice for use with a teleconverter.
Conclusion
For the entry-level Canon shooter, the Canon EF-S 55-250mm f4-5.6 IS provides an affordable way to gain image stabilization on a telephoto lens and represents a good option for an entry-level shooter or more advanced users on a budget. When coupled with Canon's EF-S 18-55mm f3.5-5.6 IS lens, you have an effective range of 29mm to 400mm with image stabilization in two lightweight, compact lenses for less than $500, cheaper than the price of some image stabilized lenses alone. Canon's alternatives tend to be pricey: the Canon EF 70-300mm f/4-5.6 IS USM lens offers a slightly different coverage range, but it's significantly heavier and will cost you at least $150 more, while the far more compact Canon EF 70-300mm f/4.5-5.6 IS USM lens costs well above the $1,000 mark.
