Tamron 17-50 VC AF Accuracy: Bad or Bad Copy ?

Started Apr 12, 2010 | Discussions thread
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mazzy80
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Tamron 17-50 VC AF Accuracy: Bad or Bad Copy ?
Apr 12, 2010

Hi,

The AF on my copy of tamron 17-50 VC F/2.8 was erratic, a lot of miss-focus, back focus.
I've sent it back to calibration.
I've get it back but I've found that the AF accuracy isn't still perfect.
The len is sharp, with no big problem on image. In focus the image looks great.

The problem is evident on the tele-end at 50m F/2.8 on short distance , where DOF is thin.
On 10 photos, only 5/6 are really on spot, 1-2 are missfocused.

Maybe it's due to the AF of my D50 that isn't that great ?
is the Tamron AF with Nikon camera not up with a Nikkor AF lens on accuracy ?
The len slight refocused between the shots even on tripod to static object.

MF the lens on the D50 I have found that the green dot in the viewfinder is lit within a little sizable zone on the focus ring with the focus point that move back or foth of course.
At the extreme point the photo are very soft/missfocused.
I don't know how the AF really work inside.

is correct to say that the AF can pick any point within the focus zone to lock, a little more tight that the reported "green zone" ? or the AF should to look for the single point of max focus ? or the D50 AF can't find it because it isn't as sensible as needed to do it ?

thanks.

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D50, 18-55, 55-200 VR, 50 1.8, Sigma 70-300 APO

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