Size... Canon EF-M mount Maximum aperture... 2.9-4 Other features... Junk I bought it new and didn't use it very often, but when I tried to use it again after a long time, it made a buzzing sound when attached to the camera, and the monitor went completely black, making it impossible to take pictures. From a layman's perspective, the exterior looks clean with no noticeable scratches. Please understand that this is a junk item.