声誉积分: 13
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I've recently had this issue, it was dropped, didn't need a new zoom key, now the autofocus seems to be hunting endlessly with no resolve, it was doing it after the drop unless the non functioning zoom ring was set to 135mm (where the lens was stuck), now no matter where the zoom is, no resolve...
声誉积分: 5.4千
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So the reason why the autofocus would only work while the zoom ring was set to 135mm (when the lens was stuck) has to do with the zoom brush. The zoom brush moves with the zoom ring and tells the lens what position the zoom ring is in. The lens needs this information to properly focus the lens. Since the lens was stuck at 135mm, if you moved the zoom ring to any position other than 135mm, the lens would be trying to focus the lens for the incorrect focal length.
As to why it's no longer focusing at all, there could potentially be a few causes depending on what's going on with your lens. Did you get the issue with the zoom fixed, or is the zoom still non-functional? Also did the autofocus just randomly stop working all together, or if you did repair the zoom issue, did it stop working only after the repair?
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I've fixed the zoom issue and that all works perfectly. The AF motor still works, but it isn't resolving on anything, I've opened the lens up and cleaned the AF prism/semi circle thing, and noticed that the little black sensor appeared cracked on top, I'm suspecting that is the culprit. Before the repair of the zoom the lens would find focus at 135mm, what's weird is that the lens will no longer find focus even at 135mm... If you have any ideas let me know.
Cheers,
Sam
@samdavison92321 If the AF sensor is cracked on top, then there is a pretty good chance that might be what's causing the AF issues.
Assuming that's the case, replacing the AF assembly would fix the issue. Technically when you replace the AF assembly, you're supposed to carry out what's called a pulse adjustment, which I believe fine tunes the phase for the AF motor. I'm not sure if it's actually absolutely necessary that this is done though, and a replacement AF assembly may potentially work totally fine without it. I just don't have the experience to be able to say for sure.
Alternatively, you could try replacing just the sensor, as I believe it's just screwed in place and might not require any soldering. Canon doesn't consider that part serviceable, so it doesn't have a part number and I'm not sure if you can find just the sensor, but you could always transplant one from a working AF assembly. This would eliminate any potential need for a pulse adjustment on the lens.
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