Initial tests with the first Tamron lens received showed that it had a substantial autofocus dysfunction similar to that reported for many lens samples in reviews on Fred Miranda.com. The lens would not autofocus accurately, but functioned acceptably when manually focused. The dealer sent a replacement lens on request. See data below. Data on the main review page is from tests with the second sample of the Tamron SP AF 17-50mm f/2.8 XR LD lens. Because others have rated this lens highly and because of variation in performance of the first two lenses, I obtained a third new sample of the lens from another dealer. Samples 1 and 2 were USA warranty models. Sample 3 was an international warranty model. All were made in Japan.

	Test shows signficant Tamron autofocus error with the first lens sample on a Canon EOS-20D camera and lenses tested at 50mm. The second lens sample received from the dealer as a replacement functioned normally and was used in all subsequent tests.
	50% MTF Performance at 50mm did not differ significantly between Sample 1 lens manually focused and Sample 2 lens with normal autofocus. Sample 3 lens does not have appreciably different function.
	Resolution performance does not significantly between lens sample 2 and lens sample 3.

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