About turning the focus dial while in autofocus... Please help!

[cameranewbie123]

First of all... I am using the Canon T7i, with the 24mm Canon pancake STM lens.

I'm a complete newbie to DSLR cameras. I turned my camera on for the first time, and it was in autofocus mode. I was trying to take a photo. The image I wanted to focus on wasn't being focused on, and I was confused. So, I turned the focus dial. The dial turned smoothly, but nothing happened. Nothing focused.

I later realized that in autofocus mode, you actually have to hold the shoot button halfway down for it to autofocus. I wasn't doing that originally; I was just aiming at something assuming it would autofocus, just like it does when shooting video. Apparently for shooting photos, you have to hold the shoot button down for it to autofocus.

So, since I didn't hold the shoot button down when I turned the dial during autofocus, does this mean that there could be no possible damage to my camera or to the lens? I guess damage can only be caused if you hold the shoot button down while turning the dial in autofocus mode?

[diverhank]

I think you were Ok in doing so.  For this lens, like other STM design, the focus is by-wire implementation - no mechanical linkage when you turn the ring.  As you stated, in order for the full time MF feature to work, the shutter button has to be half pressed.  So when you turned the ring without holding the shutter button. the movement was ignored by all.

[shadowsports]

cameranewbie123,

In addition to what diverhank mentioned, keep the following in mind.  Lenses have a minimum focus distance as well.  The 24 pancake is 6.3 in (16cm).  Objects closer to the lens than this distance will never be in focus using AF or MF. 

Video utilizes the same principle.  Focus is acquired when you depress the shutter button half way.  Capture begins when the button is fully depressed. Your camera has the ability to track subjects that move closer and farther from the camera when capturing video (auto focus).  You also have the option not to have it track if you wish such as shooting video of a stationary object. 

[Waddizzle]

There is no mechanical connection between the external focusing ring, and the internal focusing gears.  The focusing gears are driven by a motor.  

As long as the viewfinder display is active, which means the light metering system is active, you can turn the focusing ring, and adjust the focus.  When the light metering system goes idle, the viewfinder display shuts off, which shuts down the AF system, which shuts off power to the focusing gear motors, and so the focusing ring goes dead.

[cameranewbie123]

I did read in the lens instructions that I shouldn't turn the focusing ring while in autofocus, as it could cause damage to the lens or to the camera. So this is false, and I'm in the clear?

[Waddizzle]

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@cameranewbie123 wrote:

I did read in the lens instructions that I shouldn't turn the focusing ring while in autofocus, as it could cause damage to the lens or to the camera. So this is false, and I'm in the clear?

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That is good advice when the lens is in AF mode, because the camera may try activate the motors with other types of lenses, which can be damaged.  But, as long as you lens focuses in AF mode, you should be okay.

[diverhank]

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@cameranewbie123 wrote:

I did read in the lens instructions that I shouldn't turn the focusing ring while in autofocus, as it could cause damage to the lens or to the camera. So this is false, and I'm in the clear?

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For some lenses turning the focus ring in AF may cause damage if the linkage is mechanical.  Some Canon lenses have features that bypassed the limitation even though they are mechanically linked.  These are called full time MF lens...you can manually turn the focus ring while in AF.  Then some lenses (like this one that you have), the focus mechanism is not mechanically linked to the focus ring at all.  When you turn it, the lens sends electrical signal telling the camera to focus...so in this case, you can turn that ring all day without damaging anything.  You are in the clear for this lens.

[TCampbell]

This all depends on the type of auto-focus system on each lens.

Canon makes lenses with "USM" (three different variations on the USM design).  These allow full-time manual focus.

Canon makes lenses with "STM" (two different variations on the STM design).  These allow full-time manual focus.

Canon makes lenses that have a basic direct-drive DC motor.  These DO NOT allow full-time manual focus.

All lenses that have the "STM" focus motors (Stepper Motors) are focus-by-wire.  The computer reads that you are rotating the focus ring and responds.  But the computer is only watching for the ring to be turned while auto-focus is acctive which means you have to half-press the shutter button to "wake up" the system.  You can configure back-button auto-focus on most cameras ... and anything that "wakes up" auto-focus will work (not just a half-press of the shutter button).

All lenses that have "USM" focus motors have a clutch which is designed to slip.  These lenses actually do have mechanical linkage... but when you rotate the focus ring, you're really turning a ring which softly engages a clutch which is deliberately designed to slip.  This way if the camera is trying to focus AND you are trying to focus, it will slip and avoid damage.  You can focus these lenses at any time.

If the lens doesn't say either "USM" or "STM" in the name, then it likely uses a direct-drive conventional DC motor.  These lenses do NOT allow for "full time" manual focus even when in auto-focus mode.  You should disengage the auto-focus (flip the switcho on the lens barrel from AF to MF) before attemping to manually focus these lenses to avoid damaging them.

See:  https://www.canon.co.uk/lenses/tech-guide/focusing/

[MikeSowsun]

There is one type of USM AF motor used in many Canon Consumer grade lenses called Micro-Motor USM, and it does NOT allow Full Time Manual focus. Canon neglects to mention this in their general literature and you need to refer to the individual lens user manual to see which lenses are affected this way.

Most of these Micro USM lenses have front filter threads that rotate as you focus, and focus rings that spin around during Auto Focus.

These Micro USM lenses can be damaged if you were to manually turn the focus ring while in AF mode. Most of these lenses are no longer in production, but are still available on the used market.

Two examples that are still in production are the EF 75-300mm USM and EF 70-300mm IS USM.

One more still in production is the EF 50mm 1.4 and while it has Micro USM, it also has and extra clutch system that does allow FTM focus.

The EF 70-300mm IS USM user manual cautions you not to touch the focus ring while in AF mode:
 

"Do not touch the rotating parts of the lens while the autofocus is active."

 
"Do not adjust focus manually when the focus mode switch is set to AF."

I tried to post a link to the actual Canon user manual and also include a photo of the page in the manual, but each time I did my post was quickly deleted without an explanation.  Can someone explain why?