I had defended myself a long time against a mega-zoom lens, since it is known to the physics can not outwit and a larger zoom range always causes deductions and compromises in the resolution and the image defects. Therefore, I was for a while with the Canon 18-135 USM and the Tamron 70-300 USM go. Both offer a (relative to price) good image quality for each their focal range. It is also very clear that you do not have the time to convert the camera at the telephoto lens when you discover in the distance chamois on the mountain. Therefore, the Sigma 18-250mm lens was additionally purchased. It's basically a very sophisticated look and also works great on the Canon 700D. The ultrasonic motor is not quite as fast as that of the Canon 18-135, however, work on the whole very good. In order to obtain an objective comparison, I photographed with two lenses at some distance a Siemens star, which I have positioned the star again in the center and one at the edge of the image. The photos were taken outdoors in sunlight, so that the camera shake slightly, the ISO value to 100 and the panel was rather closed (typical conditions when traveling). The star takes the entire image each one about 2% of the horizontal and vertical image size of 3%. One thing is clear to see that the Sigma lens delivers softer images and especially already produces more chromatic aberration at the edge. The image resolution is only slightly worse. Implemented at the big picture (you need a while to in the first to discover the Siemens star in the big picture) but the lens will deliver wonderful pictures, so it is his destiny as a travel lens all meet.
