Usually troubles with autofocus are related to a non working AF. I've got the opposite issue: AF is working too well. Actually, it is ALWAYS working, and I cannot turn it of.
Even when I switch to Manual, when I half-press the shutter button AF kicks in. The lens can be manually focused even with AF on: if I keep the button pressed and defocus manually, it autofocuses again.
I've got two alternative fixes:
- with the "usual" set up (shutter button focuses and meters) I can press AF-ON button to stop the autofocus,
- or I can set the custom function IV-I to 3 so that the shutter button does the AE lock and the shutter actuation and the AF-ON button focuses and meters.
I have adopted the first solution which is more in line with my habits, but when using a tripod it can be incovenient (since I'm not pressing af-on and I would like my manual focus decision to be respected).
I strongly suspect that the switch is in some way broken, since otherwise the fixes would not be able to work around it, but I thought to ask here for advices/suggestion/ideas.
If it matters, the camera is an Eos 50D and obviously with other lenses the switch is respected (namely the 70-200 L, which similarly allows manual focusing when AF is on).