AF technologies

[DanK]

I stumbled on this page that explains how the various types of Canon AF mechanisms work. (Sorry, those of you who use other brands; other than the direct-drive system, I have no idea which of these are used by other manufacturers.) Some of you may have known all of this, but I didn't. I did know that the STM technology was introduced to quiet things down for video, but I didn't know that the older USM technology that is in most higher-end Canon lenses is still faster. I will find that fact useful, as I use my cameras solely for stills.

https://www.canon.ie/lenses/tech-guide/focusing/

[Manfred M]

Dan most of this is "marketing speak" as opposed to anything useful. The technology is not unique to Canon and is used by other manufacturers as well, each with their own unique marketing names given to the same technologies.

If I recall properly, the stepper motor design can support a higher duty cycle, typical of how many people shoot video. The USM works well, but is less well suited to video work (assuming one doesn't focus manually, like the pros do).

Direct drive is the oldest of the technologies.

[rpcrowe]

I can really notice the difference in speed between USM and the older AFD (ARC Form Drive) auto focus systems. This is especially noticeable when working with lenses of longer focal lengths. As an example, my Canon 135mm f/2.8 SF (Soft Focus) lens uses AFD auto focus technology. It is noticeably slower to focus than my lenses with USM AF. Additionally, it doesn't have full time manual focus capability like the USM lenses.
The only STM lens that I own is the Canon 40mm f2.8 "Pancake". It doesn't seem much slower (if at all) than my USM lenses of approximately the same focal length.
I am guessing that there may be more of a difference in AF speed between various models of USM focusing lenses and, perhaps also a difference between these lenses used on different cameras, than between USM and STM lenses as a grouping. I am talking about AF speed that is evident in real life shooting rather than that measured in a laboratory.