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Message: <blockquote data-quote="Roy C" data-source="post: 1385789" data-attributes="member: 18798">I cannot see the logic in this, a taped tc could effect the AF but why should it effect the shutter?. Even though my shutter went the AF was still working perfectly (even with a tc attached).I used both my 350D and 30D extensively with a taped tc and nothing went wrong with  those cameras!. Also I have read on other forums of 40D shutter failures on Cameras that were never used with telephoto lenses let alone taped tc's. In fact I have used a taped tc far less on the 40D than I had with both my 350D and 30DThe only reason why Canon stop AF at greater than f5.6 on these cameras is because the AF system is not good enough so therefore rather than have a lot of criticism of their AF sytem they cap it at a level they know will work fine.I would have thought that if the f5.6 cap was deactivated the Camera could be used to attempt AF at any 'f' value without detriment to the Camera - of course AF ability at f8 would be poor and f11 or greater would be utter c##p    Most peoples concern about taping tc's is that the lens hunts for focus at times and this could burn out the focusing motor - I have heard this loads of times but never seen a single post on any forum where this has actually happened, I did see a post from a 'boffin' once who stated that burning out a focusing motor was impossible.I think a more logical argument for shutter failure could be using the Camera for high burst shooting (6.5 fps) on a frequent basis as this would be directly linked to the shutter. In my case I rarely shoot long burst so I doubt if that is a contributory factor.The shutter mechanism is a relatively cheap part of the Camera (around £30) and my guess is that some 40D shutter are failing because of something simple thing like a weak spring.</blockquote>

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