This ultra-compact pancake lens for the most part is well built with 6 elements in 5 groups along with 7 aperture blades just like the bigger brother EF 50mm f1.8 STM. What does STM stand for? Step-less Motor. Manual focusing is done by focus-by-wire once you select the AF switch to MF.

Pros:
Lightweight, fast focusing lens, extremely sharp @ f4

Cons:
Higher Aberration at f2.8

However, on a crop sensor of 1.6 you'll get a field of view of 38mm, which is close to the EF 40mm f2.8 pancake on a full frame sensor. The closest focusing is 0.16m or 16cm in metric, which makes it a pretty impressive little lens and for the price...is slightly lower than the EF 40mm f2.8 STM. I've been shooting with mine for the past 2.5 years on a Canon 40D.