Das gilt meines Wissens NICHT für das EF 50mm 1,4.
... , ähnlich das alte 50 1,0 L ... Es gibt da noch ein paar Spezialkandidaten.
Bei denen wird wenn man am Fokusring dreht der AF Motor zum manuellen Scharfstellen benutzt. Anders ist es beim Ring USM wo bei den neueren durch eine mechanische Kupplung der USM direkt übersteuert wird. Bei den älteren Ring USM Optiken wird auch ein electronisches Fokus System für das manulle Fokussieren verwendet ((altes 300 2,8L, 500 4,5L ...)
Lässt sich testen indem man schaut ob sich die Optik auch bei abgeschalteter Kamera im AF Modus manuell Fokussieren lässt, das geht nur bei echtem Ring USM mit mechanischer Kupplung.
Hier der entsprechende Diskussionsbeitrag aus Photo Zone (ähnlich in meinemCanon Lens Work):
There are two forms of overridable manual focus implemented for ring USMs. One, the electronic manual focus glen mentions, is supplied on lenses like the big white telephotos.
In lenses with electronic manual focus, the focus ring causes a position signal to be sent to the lens' focus module, which then drives the ring USM motor. The nifty feature of this implementation is that Canon can provide a virtual gearbox, in a sense. You can generally choose between three manual focus speeds. Fast whips the lens around when you twitch the focus ring, while the slow speed alows very fine focus control by requiring a relatively large movement to shift focus significantly.
Then there's the "real" full-time manual focusing lenses. In these, there's an internal focus ring. On one side lies the ring USM motor, on the other the manual focus ring. Via a cute system of rings and wheels, which allow either the ring USM or the manual ring to turn the real focus ring without turning the other component, real full-time manual focusing is provided. It is manual because it is the force of your hand that physically moves the focusing group, rather than signaling to the focus module information which then turns the internal focus ring for you.
How do you tell them apart? One way is to turn your camera off and attempt to manually focus. If it does, it's the "real" manual system. If it doesn't, it's the electronic system.
I don't know offhand which lenses have the electronic form. This was the first form, developed for the 300/2.8. I believe the electronic focus module used in the 300/2.8 is identical to that in the 200/1.8, 500/4.5, 400/2.8, 600/4. They all have identical buttons for using this, down to the beeper button (boo, hiss!).
I believe the 50/1.0 also has electronic manual focusing, but don't know for sure. Perhaps others.
The "real" manual FTM was introduced to, in part, reduce cost, I believe. I think the electronic module is overkill for short focal lengths, anyway. I don't miss the lack of three manual focus speeds on my shorter L zooms with the manual form, anyway.
The above, at least, is how I understand stuff from perusing Canon's "Lens Work" (older edition) some time ago.
