The EF 50mm F1.8 II is the cheapest lens Canon makes, and the build quality is commensurate with the price. From the mount at one end to the filter thread at the other, the entire external structure is made of smooth black plastic, and overall this lens gives the impression of being built to a (very limited) budget. Features and controls are kept to an absolute minimum; you get a focus mode switch and a near-vestigial focusing ring, but that's about it. The front element is recessed by about 12mm from the filter thread, in effect providing a built-in hood for reduction of flare, and the barrel is quite broad and stubby to accommodate the focus and aperture motors plus the associated electronics.
Of course one advantage of the minimalist design approach is extremely light weight, and this lens tips the scales at a featherweight 130g, so won't exactly add unwelcome heft to your camera bag. But as the body is unusually large with respect to the optical unit itself, this has the effect of reducing the 'density' of the lens (indeed if it were a sealed cylinder, it would float in water); the overall impression is of anything but solidity.
Compared to the Canon EF 50mm F1.4 USM
Here we see the 50mm F1.8 II alongside the EF 50mm F1.4 USM, which costs more than three times as much. The slower lens is noticeably smaller and less than half the weight than its faster sibling, but that distinctly basic design approach is very evident here. In comparison, the F1.4 lens gains USM focusing with full-time manual manual focus, a focus distance scale, improved construction including a metal mount, and a bayonet fitting for the hood (not to mention that it gathers 67% more light).
On the camera
Mount the lightweight, insubstantial 50mm F1.8 on a higher-end EOS bodies such as the 5D and you could almost be forgiven for forgetting that it was even there; this is one lens which won't be a chore to carry around all day. It's perhaps best matched to the small entry-level EOS models such as the 450D, on which it forms a particularly lightweight and unobtrusive combination ideal for low-light shooting.
The lens's handling is best described as functional; the manual focus ring works OK, but it has a rather loose, imprecise feel and you probably wouldn't want to use it all the time. It is also coupled to the focusing motor when the lens is set to AF; this means that it rotates during focusing, so care must be taken to avoid holding it when using autofocus. Canon also warns against turning the focus ring manually in this mode to avoid damaging the motor or gear train, which means that full-time manual focus is not available.
This lens uses a very basic micromotor to drive the autofocus, which isn't the best system Canon has ever made. AF performance is overall quite similar to the 18-55mm kit lenses, i.e. a little slow and slightly noisy (although a lot better in this regard than some similar systems we've used, such as the Olympus 50mm F2 macro), however the large maximum aperture does mean that it continues to work happily in much lower light levels before starting to struggle and hunt for focus.
In use, the AF generally works very well in good light, but as illumination levels fall it becomes progressively more hesitant and less reliable. It has a disconcerting tendency to misfocus slightly in low light (most visible when shooting with large apertures) and whilst the camera body's AF system must share some of the blame for this, the EF 50mm F1.4 USM does appear to be more reliable in these situations. As always, it must also be noted that focus speed and accuracy is dependent upon a number of variables, including the camera body used, subject contrast, and light levels.
Lens body elements
Reported aperture vs focal length
This lens allows an aperture range from F1.8 to F22 to be selected.