I have a few STM Lenses, and the silent autofocus is great for video, looking to swap my Sigma 50mm I got the Canon EF 50mm 1.8 STM but the focus is really noisy on Eos M5 body !
Canon website says of the 50mm 1.8 STM lens "The near-silent STM (Stepping Motor) technology focuses extremely quickly when shooting photos .....Creating high quality movies is easier with STM as it delivers steady and quiet continuous focusing, so your movies are smooth, and soundtracks only capture the surrounding sounds and not the noise of a focusing motor."
This seems to be total rubbish as focus noise is very loud, which I can't understand, as it makes it useless for video, which I thought was one of the main reasons for STM ?
Comparison both on M5 body EF 50mm F1.8 STM vs EF-S 18-135mm STM lens which focuses silently, so why is the 50 1.8 STM SO NOISY ??
Looking on youtube some people report this noise, others seem to think its really quiet do the lenses differ so much ??
It seems the lens noise does vary considerably depending on which body you are using, the newer/faster dual pixel autofocus seems especially noisy, so bear this in mind, and ideally if you can find a camera store which will let you test the 50mm STM lens on your body the noise may be acceptable for your needs.