I've bought this lens used for nearly 80€, so I was not expecting the perfection. The very light and compact plastic body confirms the price impression. Nevertheless I've hoped to use it stopped down 2 steps, at f/4, on my full frame Canon 5D. At this aperture the image quality is very good except a single corner (upper left) where some blurring occur. Why? How to solve? The images below better show the behaviour. And here are some shots made with this lens: Milky Way Panorama, Cygnys, Southern Milky Way, Scorpius,