EF-S 24mm f/2.8 STM: Manual Focus override

[Scaup]

In AF mode, the manual focus override is not working. Every review of this lens that I have read states that this lens should have instant manual focus override when is AF mode. Turning the manual focus ring in AF mode does nothing even when the shutter button on my Rebel T5 is half pressed. Any explanations or suggestions are appreciated.

[MikeSowsun · Accepted solution]

Check which focus mode you are in.

 Full Time Manual Focus does not work in AI Servo mode. It is probably because the AF is continually active in AI Servo.

Here is what I have noticed with all my STM lenses:

In One-Shot Auto Focus, the focus can be fine tuned (Full Time Manual focus) anytime the shutter is half pressed. As soon as you take your finger off the shutter the STM AF goes dead. (really more like part-time manual focus) 😉

In AI Servo Auto Focus, the focus ring is always dead and you can't do manual focus over-ride or fine tune the focus.

In Manual focus, the focus ring will be active while your finger is on the shutter button, OR while the metering is active. It will also continue to operate with your finger off the shutter button, but the lens will "go to sleep" after approximately 5 seconds after the metering stops. You won't be able to focus again until you half-press the shutter and start the metering.

But......If you continually adjust the focus ring, the STM Manual Focus will continue to operate for as long as you keep moving it. (even long after the metering has stopped). If you stop adjusting the focus ring, the lens will go to sleep again after 5 seconds. A quick tap on the shutter button starts the metering again and the STM focus will operate again.

[RobertTheFat]

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@MikeSowsun wrote:

Check which focus mode you are in.

 Full Time Manual Focus does not work in AI Servo mode. It is probably because the AF is continually active in AI Servo.

Here is what I have noticed with all my STM lenses:

In One-Shot Auto Focus, the focus can be fine tuned (Full Time Manual focus) anytime the shutter is half pressed. As soon as you take your finger off the shutter the STM AF goes dead. (really more like part-time manual focus) 😉

 .

In AI Servo Auto Focus, the focus ring is always dead and you can't do manual focus over-ride or fine tune the focus.

In Manual focus, the focus ring will be active while your finger is on the shutter button, OR while the metering is active. It will also continue to operate with your finger off the shutter button, but the lens will "go to sleep" after approximately 5 seconds after the metering stops. You won't be able to focus again until you half-press the shutter and start the metering.

But......If you continually adjust the focus ring, the STM Manual Focus will continue to operate for as long as you keep moving it. (even long after the metering has stopped). If you stop adjusting the focus ring, the lens will go to sleep again after 5 seconds. A quick tap on the shutter button starts the metering again and the STM focus will operate again.

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The described behavior is probably a power saving measure. With a USM lens, the focus motor doesn't have to be active in manual mode; with an STM lens it does. So the STM lens shuts its motor down whenever it isn't absolutely necessary to have it on. The resulting inconvenience is probably one reason why there are, at least as yet, no STM lenses for Canon's professional-grade cameras.

[kvbarkley]

And with the advent of the nano-USM, there probably never will be.