Build quality of the 50 f/1.8 is very cheap (as you might expect). In fact this is the least expensive lens currently available for the EOS system. This lens feels more like a toy than a piece of optics, but has been in the lineup since late 1990. It utilizes plastic construction right down to the lens mount (the lenses are glass of course). This light material combined with the small size (2.7" x 1.6"/68.2mm x 41.0mm - W x L) puts this lens in the featherweight class - 4.6 oz (130g). The 50 f/1.8 is currently Canon's lightest and shortest lens. Considering how light the Canon EF 50mm f/1.8 II Lens is, the plastic lens mount is adequate for strength. You might get more wear than you wish if you are changing the lens frequently. With its remarkably low (sub-$100) price, it tends to attract the interest of Canon SLR users looking to start experimenting with fast lenses for low light and shallow depth of field work, or simply hoping to get sharper results than those which can be provided by the kit lens bundled with the camera body.
Although designed as a 'standard' lens for 35mm film, these days the 50mm F1.8 is far more likely to be seen doing service on APS-C format DSLRs, on which it behaves like a short telephoto portrait lens (80mm equivalent).
There is not much to this lens. There is no distance window or markings. There is barely even a focus ring - and the tiny ring that is there is barely usable.
It's also a potential option for those seeking a near-disposable lens to use in adverse conditions.
Autofocus is driven by a micro motor. Focus speed is not stellar, but fine in good light with subjects that are not moving too quickly. The Canon EF 50mm f/1.8 II Lens is one of Canon's louder/buzzier lenses - you know when it is focusing. But this is not a wildlife lens - and the noise probably won't bother most people. I suppose a positive aspect of the sound is that you know when it is working - and when focus is locked. FTM (Full Time Manual) focusing is not included. The 50 f/1.8 extends up to 5/16" during focusing - the very small 52mm filter does not rotate.
The Canon EF 50mm f/1.8 II Lens' strongest quality is its sharpness. Sharpness performance wide open (f/1.8) is decent, but the Canon 50 f/1.8 is very sharp at f/2.8 and beyond. It is slightly sharper than even the Canon EF 24-70mm f/2.8 L USM Lens.
With an f/1.8 maximum aperture, this is a fast lens. Unfortunately, only five non-rounded aperture blades are used in this lens. This design leads to sometimes-poor bokeh (image quality of out of focus areas).