I'm planning on buying a Canon 70D with the kit lens, an 18-55mm IS STM lens, to film tutorial-style videos (and for other purposes as well). I know that sometimes you can hear cameras autofocusing in video. My question is, will you be able to hear the autofocus with the kit STM lens, or should I buy a different lens that will make less noise, like a 50mm f/1.8 STM lens? I know that STM lenses are supposed to be near-silent but I really don't know anything about DSLR cameras or lenses, as I am a pure beginner. Therefore, some educated advice would be MUCH appreciated!
The 18-55 STM uses the virtually silent Lead-Screw Type STM. You will not hear it auto focus.
There are two types of STM auto focus:
The 24mm STM, 40mm STM, and 50mm STM all use the Gear-Type STM which is not all that silent or fast.
All the other EF-S STM lenses use Lead-Screw Type STM which is virtually silent and also very fast.