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The old Canon film camera EF-M, not to be confused with mirrorless cameras featuring an "EF-M" lens mount, did not have auto focus ability and was manual focus only. Does it support the focus by wire lenses in the EOS line? Does it even have any electrical connectors in the mount (apart from the ones controlling the aperture blades)?

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    It probably has electrical contacts, as the EF lenses do not have aperture ring. I don't know if it works with focus by wire lenses, though. – MirekE Mar 3 '15 at 18:11
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I don't know about the focus-by-wire bit, but this photo.net discussion thread includes side-by-side images of the mounts of a 5D and an EF-M, and shows that the EF-M did indeed have all the electrical contacts of the EOS mount.

My guess would be that manually focusing with focus-by-wire will probably still work, since that's more about electronic communication between the lens's focus motor and the manual focus ring, not about lens-to-body AF communication, which the EF-M lacks.

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  • Manual focus-by-wire only works when the shutter button is half pressed (or the AF-On back button), so there may need to be some exchange of information between the lens and camera for manual focus-by-wire to work. My gut instinct would be that one could not use manual focus-by-wire lenses with the EF-M, mainly because no such lenses existed in Canon's lineup when the EF-M was offered. – Michael C Mar 4 '15 at 4:13
  • Well, except for the 200mm f/1.8 and the 1200mm f/5.6. So maybe it will provide for manually focusing focus-by-wire lenses. – Michael C Mar 4 '15 at 4:25
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    @MichaelClark Your guess sounds better than mine. I assumed that if there was aperture control, then at least power was being fed to the lens, and that would be all that was required. But if AF communication has to be established to turn on focus-by-wire, then it wouldn't work. Trouble is that the EF-M is rare and the focus-by-wire lenses are exotics, so it's unlikely we'll find an actual usage report. – inkista Mar 4 '15 at 22:21
  • With the newer STM lenses all being manual focus-by-wire someone with an EF-M may eventually try one on it and post the results. – Michael C Mar 5 '15 at 16:36
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There are currently 2 types of Canon STM lenses: Fast and silent Lead-Screw Type STM and slow and noisy Gear-Type STM.

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The Gear type STM lenses (40mm 2.8 STM and 50mm 1.8 STM) work fine in manual focus with the EF-M, but the Lead screw type lenses (10-18mm STM and 18-135mm STM) will NOT manually focus.

(I also tried the new 18-135mm Nano USM and 70-300mm Nano USM II, and they both also do NOT manually focus on the EF-M)

SO, the EF-M works just fine with the 40mm 2.8 STM and 50mm 1.8 STM lenses, but just as with a DSLR, you do need to half press the shutter to get the metering started before the electronic STM focus will work. It works with the lens set to either AF or MF.

Once it starts working, the AF or MF will continue to work indefinitely, as long as you keep turning the focus ring. This continues even after the cameras metering as stopped. If you stop focusing, the STM will lose power after about 4 seconds of idle time. A half-press tap of the shutter button brings it back to life again.

Image Stabilization is a different story as it does not appear to work at all.

I also tried using my old EF 35-80 Power Zoom lens on the EF-M, and the power zoom function DOES work. But, because this lens has no manual focus ring, the lens of course is not really usable on the EF-M.

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