Electronic full-time manual focus - does it wear out?

As I understand all big lenses have electronic FTMF, therefore if AF breaks for some reason, the lens will not focus at all. I have heard some reports about USM beeing worn-out. Does it happen? How long are these big lenses serviced after they are discontinued?

Also, in cold I tried often to prefocus manually to save batteries, especially from infinity to close range and vice-versa. Is manual focussing on the lenses with the electornic FTMF more efficient than autofocus, in terms of energy consumption?

Thanks,
Fero

When you are focusing one of the USM or AF-S or HSM lenses the autofocus is done via waveguide motors and is not done through mechanical means in the traditional sense as it is in older autofocus types. Since there is no mechanical coupling of gears to a motor one can focus manually and electronically without having to throw a switch to disengage the mechanical gears. USM doesn't wear out as there is nothing really to wear out however some of the electronics can fail as can any other electronic component in your image making system. These types of motors are orders of magnitude more reliable than mechanical motors and can usually withstand things like being dunked in water - once dried out, the AF motors come back to life although some of the circuitry in the camera attached to the lens may not.

Manual focus is achieved through the use of a light clutch mechanism that engages when the focus ring is turned. This manual focusing does not consume any power.

Thank you EJ!

I thought that MF here works that by turning the autofocus ring you just send the info to the AF motor and the actual movement of the focusing parts is done by the USM motor itself?

Fero

No the USM motor is not used when manually focusing.

In many of the older "L" series lenses (EF 200mm f1.8L, EF 300mm f2.8L, EF 400mm f2.8L, EF 500mm f4.5L, EF 600mm f4L, EF 85mm f1.2L, and the EF 28-80mm f2.8-4L), the USM motor is used for manual focusing as well as autofocus, and consumes power in doing so. Of the lenses currently in production, only the 85mm f1.2L has this design (and I believe it has recently been discontinued as well).

These components do fail (although I don't know if you can call it "wearing out") and I have had to have the USM motors replaced on several lenses I've owned, including big lenses like the EF 300mm f2.8L's.

Thanks Cliff, just curious - how much does it cost to replace a USM motor?

It's actually not that expensive on a big lens (relative to the cost of the lens, anyway). I pulled out the repair invoice for my EF 300mm f2.8L from December 1999, and the cost was C$180. I'm a CPS member, and that price included my 20% CPS discount.

I've also had to have the USM motors replaced on a 20mm f2.8 USM, a 28-105mm f3.5-4.5 USM, and a 28-135mm f3.5-5.6 IS USM. The cost for the work on these consumer-grade lenses was not much lower than it was for the 300mm f2.8L.

Thank's a lot,

now I am just thinking for how long they have enough spare parts. I am planning to buy one of these older big "L" lenses. If I remember correctly I think all the producers should be able to service their products for 5 years after they stop the production. I think the best would be to call Canon.

I just called Canon Canada, they service they lenses 8 years after they are discontinued.

Fero