Auto Focus Problems

jonathanbp (e2 Member)

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12 Feb 2011 - 12:35 AM

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Hi,

I use a Canon D50 with a Sigma 18-200 lens. Both are 2 years old, have taken 7,500 images to date with the equipement.

I'm wondering if anyone has had a problem with degredation of the autofocus? When I first bought the camera my images were pin sharp, now, not so. Does autofocus degrade after a while? Is the the lens or the camera? Are digital cameras supposed to be taken in for a 'service' once every 5,000 pics or so? I'm furstrated...sometimes it works, other times, no so.

Any tips appreciated.

timbo

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12 Feb 2011 - 10:40 AM

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And possibly a service.
I have found with Sigma lenses that after a while they do appear soft and in some cases badly soft. Sent to sigma who serviced them but never really happy afterwards so tend not to use them now.

discreetphoton (Site Moderator)

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16 Feb 2011 - 10:13 AM

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partly it will be down to the difference in depth of field with full-frame, which allows for better edge contrast in your F90.

LenShepherd (e2 Member)

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17 Feb 2011 - 9:36 AM

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Quote: When I first bought the camera my images were pin sharp,

First clean the lens and body contacts - then do an AF test of a good AF target, ideally using flash as the main light source, and camera on a firm tripod. Shooting this way can you get very sharp images?
If not, providing your subject is one the AF can accurately detect, your camera or lens needs a repair.
If your camera AF is good in a static test maybe you now shoot different subjects beyond the AF capabilities of the camera and lens.
Turning to film bodies v digital - there is no AF speed difference with a good contrast target between my F5 and my D3s using single are AF
The D3 can detect a much lower contrast target than the F5, and in 51 point AF the D3 slows up because it is processing more information than in single area AF.