The main difference between the 18-55mm and 18-135mm lenses is their focal length range. The 18-55mm lens has a shorter focal length range, making it more suitable for wide-angle shots, while the 18-135mm lens has a longer focal length range, allowing for more versatility in capturing both wide-angle and telephoto shots. In terms of performance, the 18-135mm lens generally offers better zoom capabilities and image quality compared to the 18-55mm lens.