Lens Variation Facts and Fallacies - Is it the lens or something else?

[Jay Gould]

dpreview has always been one of the Gold Standards for photographic information; have a read of this interesting article:

http://www.dpreview.com/articles/7333489584/variation-facts-and-fallacies

[Paul Granone]

HAL9000: It can only be attributable to human error.

[Ian Cassell]

Thanks, Jay. That IS interesting and educational.

[Chris Brennan]

I've always enjoyed reading Roger Cicala's articles. He truly has gift in outlining what could be boring subjects, and making them interesting! And, he clearly knows what he's talking about!

[Flavio Rose]

I would keep in mind that Amazon.com (owner of dpreview.com) -- and to a lesser extent lensrentals.com (Cicala's outfit) -- have a financial interest in propagating this information, namely to reduce customer returns which are often made because the customer believes that the lens is soft.

I have drawn from Cicala's articles a conclusion perhaps different from his, namely that with so much variation in sharpness, it makes sense to try to get an exceptionally sharp copy (when buying, not when renting). Unfortunately for Amazon.com, the only feasible algorithm for getting an exceptionally sharp copy from them is to buy, test, and return iteratively until a really sharp copy shows up.

I am also skeptical of Cicala's information about variation when you test the same lens with different copies of a camera. For all that he has been willing to disclose, the variation he reports could all be due to the well-known variability of phase difference autofocus. That variation is just avoidable noise in the measurement; to seriously test the sharpness of a lens, you need to use live view manual focus or, at a minimum, to microadjust the camera for the particular lens you're testing (something Cicala recommends).