Q. How many copies of a lens do you test for a review?

Results are normally derived from a single lens. It's not practical for us to test multiple samples of a lens as a matter of rule - it would simply take far too long.

Q. So how do you know if you have a good copy?

Our analysis software provides us with more information than reaches the reader of the review. We measure the sharpness across the four diagonals of the frame, before averaging the results for the final data. This shows us whether there is any significant asymmetry, which is a good predictor for whether we have a 'good' or 'bad' copy. When we have a clearly problematic lens, we reject it and request a second copy for test.

Q. Can I compare results obtained using different test cameras?

Strictly speaking, sharpness results should not be directly compared between tests carried out using different DSLR bodies, as the camera itself influences the results. Most notably, results get unreliable close to the Nyquist frequency due to the effect of the camera’s anti-aliasing filter (this is why the Nyquist line is explicitly marked on the graphs).

However, all of the other results (chromatic aberration, distortion, and falloff) should be directly comparable regardless of the camera body used, and we’d stress that these are equally as important as sharpness in evaluating the overall performance of a lens.

Q. Will I really see the difference between lenses if I don’t print large or pixel peep?

If you normally view photos full screen on your computer (as opposed to pixel-peeping at 100%), or only print relatively small (6” x 4” or 7” x 5”) you won’t see a huge effect from differences in sharpness, or much colour fringing from chromatic aberration. However, you will still see the effects of distortion and falloff no matter how you view your pictures.  

Q. I can't see the lens review widget in my web browser, but get a blank space instead. What's the problem?

The widget requires Adobe Flash Player to operate, so you may need to update to the latest version or uninstall/reinstall if you're having problems. If you're using Flash blocking software (and given the number of bad flash-based sites in the web we can forgive you for this), you'll need to add www.dpreview.com to your list of allowed sites.

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