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I'm using a Canon 1100D body with a Tamron 70-300mm lens, and I've recently been getting the Err 01 message.

This happens on full zoom with the camera set to anything other than aperture priority. I've cleaned the contacts to no avail. If I back-off the zoom, it works. If I partially uncouple the lens (to the point where the auto-focus ceases to function) it works.

Is my issue still dirty contacts, or likely to be a failing connection within the lens? Does aperture priority use different contacts so the failing ones don't cause a problem?

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    Not an answer, only an idea: as this problem only occurs at full zoom, it might be a mechanical problem, e.g. some friction in the aperture mechanism being worst with the full-zoom configuration, some nearly-broken internal lens cable or similar. As the camera-lens mount isn't affected by the zoom level, I don't suspect that to be the problem cause. – Ralf Kleberhoff Apr 29 at 10:31
  • When you use aperture priority, is the aperture always set to the widest available setting (lowest available f-number)? – Michael C Apr 30 at 0:13
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What you describe is often caused by ribbon cables inside the lens beginning to crack so that continuity along one or more of the channels is lost only when the cable is in certain positions.

Without knowing what aperture settings are selected when the camera is set to Aperture Priority, it's difficult to draw much from the fact that you do not experience the issue when using Aperture Priority.

If we can assume that you've always got the aperture set to the widest available setting (lowest available f-number), then that would remove the need for the camera to send an instruction to the lens to stop down. It would also remove the need for the lens to confirm to the camera that the aperture diaphragm is now in the requested position. So it may be that the issue is caused when the lens attempts to stop down the aperture diaphragm or when it then attempts to confirm the position of the aperture diaphragm immediately before taking the image.

In your case, this inability to stop down and/or confirm the position of the aperture diaphragm seems to only occur when the ribbon cable the main PC board in the lens uses to communicate with the aperture diaphragm assembly is in the position it is in when the lens is in the fully zoomed position.

Based on the fact that the lens works fine when not fully zoomed, we can eliminate the possibility that it's an issue caused by an older third party lens that has been reverse engineered to work with existing camera models available when it was designed but does not work with newer camera models that might have introduced parts of Canon's lens-camera communication protocol that wasn't used by the older models. I've got a 1990s vintage Sigma 70-300/4-5.6 that works fine with my EOS film camera but only works with my EOS digital bodies if the aperture is set to the wide open position, regardless of the focal length.

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  • Worth noting that "wide open" with that lens depends on how far zoomed it is, so without knowing the details of the protocol, there's still a possibility that the error occurs because of some bug in the way the lens reports its maximum aperture and/or how it replies when asked to open it wider than is allowed in a given zoom position. That said, my money would still be on the aperture ribbon. :-) – dgatwood May 5 at 23:12
  • @dgatwood The size of the actual aperture diaphragm rarely moves when those class of lenses is zoomed. It's wide open at 70mm and f/4, it's still wide open at 300mm and f/5.6. The effective aperture changes due to not all of the change in magnification being between the physical aperture and the front of the lens. The different f-number is because only about 71% of the magnification between 70mm and 300mm occurred in front of the aperture diaphragm. The other 29% of the increased magnification is the result of lens element movement behind the diaphragm, affecting the exit pupil size. – Michael C May 6 at 9:09
  • So the entrance pupil (effective aperture) only grows from 17.5mm at 70m and f/4 to 53.6mm at 300mm and f/5.6. In order to maintain f/4 at 300mm, the entrance pupil would need to be 75mm wide. For that to happen, all of the increased magnification when the lens is zoomed from 70mm to 300mm would need to occur in front of the physical aperture diaphragm and none of the increased magnification could be due to lens movements behind the diaphragm. – Michael C May 6 at 9:13
  • Sure, but I'm assuming that the camera is still saying "Give me f/[x] aperture," not "give me [x] stops below wide-open," which is to say that if there were a bug related to how the lens replies when asked to open up wider than it can open, that could ostensibly manifest itself in the form of an error at longer focal lengths even if the aperture isn't moving. That's all I'm saying. :-) – dgatwood May 6 at 22:07
  • With Canon's electronic communication between camera and lens, which encompasses every EF lens ever made, the camera won't let you request, say, f/4 when the lens is at 300mm and wide open at 300mm is f/5.6, just as it won't let you set f/2 with an f/4 lens. With pre-electronic communication lenses, a lens with an aperture ring would remain fixed at f/4, but the photographer was to one who needed to know that at 300mm the f/4 position was actually f/5.6. But that's totally not applicable to a Canon 1100D. – Michael C May 6 at 23:43

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