@calcloverling wrote:
Does focusing a lens in AF break a lens? I don't think I've ever done this but it crosses my mind in case someone else using my camera has by accident...
Is there something about a 50mm lens that is more prone to breakage? I've had 2 in several years that no longer focus.
Whether a lens can be safely focused manually with the AF turned on depends upon the type of auto focusing drive motor it uses. Unfortunately, Canon has made 50mm lenses with all three types: micro motor, STM and USM. That's why previous responses have asked exactly what lens(es) you have used.
Micro motor lenses can be damaged by manually overriding AF. You need to turn off the AF before manually focusing. Examples of this are the older Canon EF 50mm f/1.8 first version and the EF 50mm f/1.8 II. The Canon EF 50mm f/2.5 Compact Macro is another micro motor lenses. It's safe to assume any auto focusing Canon EF, EF-S, EF-M or RF lenses that aren't marked "STM" or "USM" are micro motor lenses. (Obvious exceptions: purely manual focusing lenses such as the TS-E Tilt-Shift, MP-E 65mm 1X-5X Macro and RF 5.2mm Dual Fisheye 3D VR.)
STM (stepper motor) and USM (ultrasonic motor) lenses are not harmed by manually overriding AF.
In fact, STM lenses are "fly by wire", which means they electronically detect the movement of the ring and use some sort of servo to move the focusing element, so they have to be powered up before you can manually focus them. If the camera is off or in sleep mode and you turn the focus ring, nothing happens. An example of this is the current Canon EF 50mm f/1.8 STM. (Note: This will never be a problem with the mirrorless lenses, either the EF-M or the RF series, because those cameras always need to be powered up anyway for their electronic viewfinders and/or rear monitors to work.)
Most USM lenses can be manually focused at any time, powered up or not. There are some exceptions though. A few are "fly by wire", too. And, at least one of them is "hybrid USM"... the Canon EF 50mm f/1.4 USM. There have been rumors over the years that it's AF system is somewhat fragile and overriding it manually might eventually cause it to fail. Some have also noted that a hard bump on the focusing ring or the front barrel when it's protruding (i.e., the lens is focused very close) might damage the AF system of this particular lens. I have to say, though, that I've got one that I bought used many years ago and have used fairly often with no special treatment without any problems. It's possible this is because I always use it with the bayonet hood... which covers and protects the focus ring when the hood is reversed for storage and protects the front barrel when in use. That's a theory,. Or maybe I just "got a good one".
Their EF 50mm f/1.2L USM is the type of ultrasonic "ring" motor that Canon calls "FTM" or "full time manual"... safe to focus manually at any time. Most Canon USM lenses are this type. Some newer models use "Nano USM", which appears to also be "FTM" capable.
In addition to their differences with respect to manual focus...
- micro motor lenses also tend to be slower focusing, noisier and may be less accurate
- STM lenses are faster than micro motor, accurate, quiet and smooth operating, ideal for video
- USM is even faster still, as well as accurate, but makes a little noise and may be too abrupt for video.
- Nano USM is both quiet and smooth like STM, as well as fast and accurate like USM.
For what it's worth, the only Canon lens I'm aware of that's been made in versions with all three types of focus drive is the EF-S 18-135mm. It was initially offered with a micro motor. Then along with some optical changes a faster focusing version with STM came out. Finally it was offered apparently with the same optics, but an upgrade to USM focus drive. In fact, it was the first lens to use Canon's then new Nano USM. Canon claimed this was 2X to 4X faster focusing than the STM version.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2), EOS M5, some other cameras, various lenses & accessories
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