Quote: Then consider if you want really a SDM lens or not. The recent survey might help:
Maybe it's you that needs to read it....
Quote: *Despite the relatively large sample size, due to the likelihood of response bias, these figures should be treated as relative measurements rather than an absolute failure rate
All mechanical devices fail eventually. Unless you're going to go to manual focus it's certainly going to happen that your auto-focus is going to stop working one day. As will the screw drive motor in the screw drive cameras.
So yes, if you never want to be affected by an AF motor failure, go back to manual focus. AF may in fact be not nearly as cost affective, compared to MF just as riding a bike is a lot more cost effective than driving a car, if you can get where you are going on a bike. If it's makes you're life easier, it's not free. The more complicated things are, the more things there are to go wrong. That's almost as certain as taxes and death.
I love my one SDM Lens. It's quiet, focuses quickly and hasn't given me anything but great pictures. SO, you can avoid SDM if you choose, but you might be missing out on something you'd really appreciate.
I'm thinking about a Tamron 70-200 but I've noticed in forum reviews it has about a 10% failure rate. ( But if you get a good one, there is a 0% failure rate. People who have trouble , have it right out of the box.) Sounds to me reading the reviews any lens that makes odd noises should be returned. The Tammy is a screw drive, so I'm not convinced this is an SDM issue. As pointed out in other threads, if the lens is binding anywhere in it's focusing range, the motor is going to get overloaded and fail. It's the squeaky thing that is the problem here. Any lens that has mechanical problems, screw or SDM is going to fail sooner than later... because the internal components are being stressed beyond spec. go with that and return the lens. A lens that makes odd noises is almost certainly stressing the motor. It takes energy to create those noises.