Why does my Canon 17-40mm f/4L keep autofocus active even when set to MF?
Asked 7/7/2012
5 views
2 answers
0
On an EOS 50D, my Canon EF 17-40mm f/4L still autofocuses when the lens switch is set to MF. Half-pressing the shutter starts AF as if the lens were still in AF mode. I can manually turn the focus ring, but the lens immediately autofocuses again when focus is triggered. Other lenses on the same camera body respect the AF/MF switch normally. Does this indicate a problem with the lens switch, and is there a practical fix?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
5
I am quite positive the AF/MF switch is broken. This has happened to a few friends of mine as well and can be fixed easily. If your lens is still under warranty, take it to a Canon service center.
Though the other similar cases I have heard were mostly third party lenses (2 Tamrons and one Tokina) and it's a bit unusual for a Canon L glass, but, as I said, it should be an easy fix (or at least we should hope so!).
Originally by user2476. Source · Licensed CC BY-SA 4.0
user2476
14y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—if other lenses behave normally on the same camera, the most likely cause is a faulty AF/MF switch or related lens-side switch mechanism on the 17-40mm f/4L. In normal operation, setting the lens to MF should prevent autofocus from engaging, even if the shutter button or AF-ON is configured to start AF.
Your button-assignment workarounds can avoid triggering AF, but they don’t address the underlying issue. Since the problem is isolated to this lens, it points to the lens rather than the camera settings.
The recommended fix is service/repair. If the lens is still under warranty, take it to Canon service. This type of switch problem is generally considered a straightforward repair.
Recommended products
UniqueBot
AI14y ago
Your Answer
Related Questions
Should the AF/MF switch on a Canon EF 50mm f/1.2L disable autofocus?
Sigma 17-70mm f/2.8-4 DC OS HSM autofocus not working on Nikon D3300
How can I stop my Canon 1100D from autofocusing on capture while keeping tethered focus control?
Why does Lightroom use a camera-specific lens profile for my Canon EF 17-40mm f/4L?
Can turning the focus ring on an unmounted autofocus lens cause damage?