topic Re: Lens STM focus motor fighting against pressure asserted to front of lens in EF & RF Lenses

RF28mm F2.8 STM focus motor fighting against pressure applied to front of lens

Hobby-Snapper — Sat, 10 May 2025 12:42:30 GMT

I have an RF 28mm f2.8 STM lens which I love for its small size and weight.

My concern is that I offten refit the lens cap while the camera (R5 MK2) is still powered on and the focus motor 'fights' agains the pressure of re-fitting the lens cap. The motor makes an unpeasant noise and vibration while briefly fighting against the pressure.

My question is: Is there any likelyhood of damage or excessive ware on the AF motor and its gear train?

Thanks in advance for your thoughts.

Re: Lens STM focus motor fighting against pressure asserted to front of lens

Erica407Den — Sat, 10 May 2025 09:20:23 GMT

Hello!

Refitting the lens cap while your Canon RF 28mm f/2.8 STM lens is powered on can cause the focus motor to resist, leading to noise and vibration. While short-term resistance is unlikely to cause immediate damage, repeated pressure against the motor could lead to excessive wear on the AF motor and gear train over time.

To minimize potential strain, consider turning off the camera before refitting the cap, allowing the focus mechanism to reset properly.

Best Regards,

Erica

Re: Lens STM focus motor fighting against pressure asserted to front of lens

Waddizzle — Sat, 10 May 2025 12:34:21 GMT

There is a setting in R Series cameras that controls whether or not the camera tries to maintain focus between shots, even if the metering system is inactive. Canon has changed the name of the setting in different models for some reason. In most cameras it is called “Continuous AF”.

Most users disable this setting because of the battery drain. This is setting is also joined at the hip with Pre-Capture, used with Continuous Drive mode and Servo AF. I keep these settings disable in my R6 Mark II. If you have these settings enabled, then you might try disabling.

Lastly, I do not replace the lens cap back onto the lens until I turn the camera off.

Re: Lens STM focus motor fighting against pressure asserted to front of lens

Hobby-Snapper — Sat, 10 May 2025 15:31:04 GMT

Thanks for the reply. I never use servo auto focus on the R5 so the focus motor only activates on shutter button press.

Basicaly, even though the lens is not actively trying to focus, the focus 'system' is trying to hold the lens in that last used focus position.

I have tried remembering to turn the camera off before re-fitting the lens cap but I often forget!!

I'm just wondering if I am likely to be causing in stress to the STM motor and mechanism when it tries to fight my pressure to the front of the lens - the noise and vibration it makes is a bit concerning!

Re: RF28mm F2.8 STM focus motor fighting against pressure applied to front of lens

Waddizzle — Sat, 10 May 2025 15:53:54 GMT

There is another setting that “Retracts Lens On Power Off”, or something like that.

Re: RF28mm F2.8 STM focus motor fighting against pressure applied to front of lens

Hobby-Snapper — Sat, 10 May 2025 15:59:45 GMT

Yes, I have this turned on (retract lens on turn off) and it works although it takes a few seconds after turning off before it retracts the lens. My problem is that I often forget to turn the camera off (and wait a few seconds for the lens to retract) before fitting the lens cap....