The Canon 50mm f/1.8 II has fantastically good optics, better than Canon's "L" series wide lenses like the 16-35mm f/2.8 L II.
In fact, this N39,900 plastic lens gives sharper results than the 50mm f/1.4 USM I've used, especially in no light. The f/1.4 is soft at f/1.4, and worse, I rarely get in-focus results with it, while this f/1.8 lens is sharp at f/1.8, and always delivers perfect in-focus results!
The 50mm f/1.8 II weighs less, costs less, and autofocuses more accurately than the 50mm f/1.4 USM.
Try to hate this plastic-mount made-in-Malaysia 50mm f/1.8 II, but when you look at the images, you'll be convinced. The mount is plastic, but the glass is all Canon's finest multicoated glass.
How can this cheap lens be so good? Simple: every time you ask a lens to do more, like to be faster, to be wider, to be longer, to offer instant manual-focus override, or especially if you ask it to zoom, a lens has to get bigger, heavier, more expensive, more distorted and/or less sharp. Lens design is always a compromise among these trade-offs.
When you ask for a non-zoom, fixed focal length normal lens of only moderate speed, it's easy to make the optics fantastic, and at a very, very low cost if you don't mind plastic.
Did I say "only moderate" speed? Even though it's only moderate as fixed lenses go, f/1.8 is still over a stop faster than any Canon EF zoom. This f/1.8 lens lets you shoot at ISO 800, while in the same light you'd need ISO 4,000 with the 24-105mm f/4 L IS to get the same shutter speed! f/1.8 lets in five times more light than an f/4 lens. This 50/1.8 is also less than one-fitth the weight and less than one-tenth the price of the 24-105mm, and has only half the distortion!
This 50mm f/1.8 II uses the same optics as the original 50mm f/1.8 EF of 1987. The 1987 lens used a metal mount and had a focus scale.