It is very sharp, it is very fast, it is very well built and it is one of the least expensive L lenses Canon makes. It is the highly regarded Canon EF 135mm f/2.0 L USM Lens. If 135mm is the focal length you need, you will not be disappointed by the Canon EF 135mm f/2.0 L USM Lens.
Look into the end of this lens and you see what seems like an unusually large amount of glass. From the looks of the resulting images, it must be really good glass.
The Canon EF 135mm f/2.0 L USM lens is renowned for its image sharpness. More specifically, the 135 L has decent sharpness at f/2.0 with sharpness increasing to impressive at f/2.8. Especially impressive is this lens’ corner sharpness where it puts most zoom lenses to shame. APS-C (1.6x) body users will find corners razor sharp at f/2.8 and stopped down to f/4, the entire full frame image circle is extremely sharp.