Canon EF 50mm f/1.8 lenses

introduction

version II was introduced in 1990 as a budget standard lens - “nifty fifty” or “plastic fantastic” - cheap, ultra-light, and nasty design, poor handling but optically very good for the money if you shoot at f/2.8-5.6 - but even then the corners never get sharp, wide open, even the centre is not sharp
version I has same optical formula but better build quality
a newer STM version has better build, better AF and more blades and is sharper in the corners
which 50mmm lens to buy?
- the 50mm f/1.2L gives shallowest depth of field (DOF)
- the Canon EF 50mm f/1.8 lenses is much cheaper, more accurate AF, and sharper than the Canon EF 50mm f/1.4 USM lens
- perhaps the best compromise is the Sigma 50mm f/1.4 ART

50mm f/1.8 lens
6 elements in 5 groups
better build than the II version
7 blades instead of 5
metal mount not plastic
designed for lens hood (ES-68) which can be stored reversed on the lens
wider MF ring and focus by wire giving full time MF but means you can no longer retract the lens when camera is OFF
AF motor is now a “near-silent” although still audible, CDAF optimised stepping motor which gives faster, more accurate AF than on the II version