The EF-S 17-55mm f / 2.8 IS USM, with a constant f / 2.8 aperture over the entire zoom range and 3-step image stabilizer, provides excellent low-light shooting performance and flexibility. The EF-S 17-55mm f / 2.8 IS USM, which has an effective focal length range of approximately 27-88mm (35mm equivalent), is a powerful lens that delivers remarkable image quality. Wide zoom lets you capture more from any scene and add a new sense of space and perspective to your photos. The EF-S 17-55mm f / 2.8 IS USM features Canon's 3-step Image Stabilizer (IS). Image stabilization, ideal for handheld shooting, allows you to use a shutter speed up to 3 steps slower without noticeably increasing image blur. Image stabilization is also helpful in low light, fast-paced scenes and capture from moving vehicles. The lens transmits distance information back to the camera's E-TTL II flash system to ensure optimal flash metering in all shooting conditions.