The difference between Canon EF 50mm f1.8 II and EF 50mm f1.8 STM lenses

The optical quality between the two is very similar. In both cases you’re going to get as sharp a lens as you’re going to get without paying several times more, a MAJOR upgrade from a kit lens or a super zoom or something, but not exactly Zeiss or anything. Both can have some issues in the corners, but that shouldn’t be too relevant if you’re on a crop sensor. If you’re not on a crop sensor, what are you looking at budget lenses for? Go pair it up with some L glass!

The STM motor is quieter, smoother, and faster than the motor on the II, so you’ll have better and more reliable focusing.

The mount on the STM is metal, not plastic like the II. I think most of the rest is still plastic, though.

The aperature blades are better designed on the STM, so you’ll get better bokeh, especially when it comes to bright points of light shot not quite all the way open. Those tend to be pentagons on the II, slightly rounder on the USM. Funny enough, the Yongnuo, while being mostly a knockoff of the 50mm F1.8 ii, has an aperture more similar to the USM. None of them have great bokeh though, as you’d expect for a budget lens.

If you’re price-sensitive like me, the II is still a very high performer for the price. I recently snagged one used for $50 US, while the USM rarely seems to go for much less than $100. The Yongnuo also got decent reviews overall for what it is, and that can be had even cheaper, but horror stories about quality control scared me off. If the price difference doesn’t bother you, the USM has a few nice bonuses, with the sturdier mount and better motor, and is also still available new. Really, none of the differences are going to be super critical- they both perform well for the price. The next step up is the 50mm f1.4, but it’s a lot more expensive and isn’t really any sharper, but that wider aperture gives you a shallower DoF and the bokeh is improved.