Helping a friend find a lens for their daughter. They have a 550D. Looking for a 50mm lens.
Question is, how are the current 50mm f/1.8 STM and 50mm f/1.4 USM, compared with each other, both in build quality and in photo quality at the same aperture (f/1.4 isn't really significant in this case)?
define photo quality.
I had 50 STM, at some point replaced it with the 50/1.4
to my eye both are great for their intended purposes, ie. people, pets, plants at f<=2.8 and views/details at f>=4.0. meaning I don't have issues with things like corner sharpness at big apertures as the photos I take at f/2.8 will have nothing within DOF in the corners. while when I switch to f/4.0 or higher value, then it's a subject requiring more DOF and corners will be plenty sharp by then.
major difference is in bokeh and general image. 50 STM has bubbly bokeh with modern look and quite some micro contrast. 50/1.4 is very old school (a real double gauss) with much less microcontrast and pleasant but sometimes more "geometric" bokeh (don't know how to describe it).
I prefer the old school imaging of 50/1.4 but can easily imagine that most people born in 21 century wouldn't really get why
build quality wise - so-so for 50 STM, very under-par for 50/1.4. STM lens is pretty dense built and feels relatively solid in hand, but it's actually a lot of plastic and lacks any sealing along focusing ring etc. so if you keep using it in dusty conditions you will notice it for sure. 50/1.4 has all those issues and also crappy feeling in hand. for many people it's one of the reasons to avoid this lens. some people who love this double gauss (myself included) swear to always carry lens hood on this one, as part of protection of the retracting front lens group against the bumps which are told to be main reason behind EF 50/1.4 deaths.
Also how do they compare with the old 50mm f/1.8 (I don't think it had anything in its name beyond that?) or the II model? I'm familiar with those and the EF 50mm f/1.2, but not the two mentioned above. Is the STM model significantly better? Does it have a quiet(er) focus motor (the old 50mm was terrible, like a Transformer at the dentist)?
50 STM has near-silent AF. STM is optimized for smooth lens travel so it's not as quick as proper USM but FWIW, you wouldn't even notice it on the 550D with it's older AF system.
50/1.4 doesn't actually have a proper USM motor as it's name indicates, but some form of drive which is in between old AFD and proper USM. technology aside - it's whooshing (by far not as loud as old AFDs, but you can clearly hear it), it's not really as snappy as proper USM, but it's relatively fast
FWIW, I think 50 STM is safer option for someone younger. a bit sturdier built, more modern imaging, size-weight more matching a 550D (especially if you consider always having lens hood on 50/1.4).