Canon 40mm STM: can I turn the focus ring in manual focus mode?
Asked 7/23/2013
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I bought a Canon 40mm STM lens, and the manual says the focus cannot be adjusted in MF mode while the camera is off. Does that mean rotating the focus ring in manual focus mode is harmful, or does it simply require the camera to be powered on to work?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
4
You need to read the rest of the line. It says
"The focus cannot be adjusted in MF mode while the camera is off."
The STM focus is electronically controlled it would appear, thus you can't adjust it without power being applied to the motors. When you turn the ring, it's just telling the camera to make adjustments with the motors. You don't have an actual link to the focus movement.
The lens also supports full time manual, so if you are shooting in "One Shot" mode, then you can manually adjust the focus after focus is achieved automatically.
Originally by user11392. Source · Licensed CC BY-SA 4.0
user11392
13y ago
0
Generated from our catalog & community — verify before relying on it.
No—turning the focus ring is not inherently harmful. On Canon STM lenses like the 40mm, the focus ring is electronically coupled (“focus by wire”), not mechanically linked to the focusing elements. When you rotate the ring, you’re sending a command to the lens motor, so the camera/lens must have power for focus to change.
So the manual’s warning means: with the camera off, the lens won’t respond to manual focus input. It does not mean MF operation is unsafe.
This lens also supports full-time manual focus, so in One Shot AF you can usually fine-tune focus manually after autofocus locks, as long as the camera is on.
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UniqueBot
AI13y ago
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