Not for the faint of heart - DIY 350D backfocus fix

Started Dec 1, 2007 | Discussions thread
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RobertoAvanzi
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Not for the faint of heart - DIY 350D backfocus fix
Dec 1, 2007

Shortly after buying the 70-200 L IS f4 I noticed that the focus was not spot on, and that the lens had a bit of backfocus. I was not really noticing it on the 17-85 IS - the lens is not that sharp anyway, I though, and at those focal lengths and such slow aperture the subject was always almost completely in the focus range. I attributed the problems with the SIGMA 30mm f1.4 at apertures below 2.8 to its famous erratical behaviour. And I still had enough keepers.

But recently, things got worse (AF drift?) and the 70-200 was able to pinpoint the symptoms of the illness.

Printed some focus charts, all lenses were backfocussing by more or less the same amount. Went to the shop (not the one where I bought the camera, but the one where I bought the 70-200), tried my lenses on a 40D body, also not perfectly calibrated it seems, it was front focussing by at most 1 mm, nothing to bother about, in fact, except perhaps for some macro work (that I do not do). But, the 350D was systematically backfocussing 20 mm with the Sigma at 30 mm, about 16 mm at 70 mm with the 17-85 AND with the 70-200, and still around 12 mm at 200.

Canon in Willich was treating me in an arrogant way on the phone (no we do not have a price list for fixing AF problems on cameras and lenses), the shop where I bought the camera refused to help me (that's one reason more to stay with the new one), and then I remembered this

http://www.astrosurf.com/buil/autofocus/adjust.htm

Since I already decided to buy a 400D for the imminent travel, and later to have the 350D fixed and then ebayed, I decided to try it.

Finding two allen keys for 1/20" in germany is not easy, here is all metric, but I was lucky.

Not for the faint of heart. Waving an allen key in front of the sensor is not what you always wanted to do. Touch it and you are boned. And you have to exert some force while turning, and you hear some clicks.

The result? Now the camera is focussing MUCH better. A bit of front focus (but the other closest setting had a slightly bigger back focus), but something like one mm at the fastest setting on the 30mm sigma, and a couple of mm at 200 mm on the L zoom, nothing noticeable on the 17-85 IS.

Now, I am exhausted. Tomorrow is (weather permitting) another shooting day! The purchase of a new camera is delayed. I hope I can wait for the 40D successor and devote next year's budget to glass. A wide angle (The canon 10-22 or the new fast tokina 11-16) is due!

Roberto

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Canon EOS 40D Canon EOS 70D Canon EF-S 17-55mm f/2.8 IS USM Tokina AT-X Pro 11-16mm f/2.8 DX Sigma 30mm F1.4 EX DC HSM +3 more
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