Focus Fallibility: Lens Test Fallacies

Focus Fallibility: Lens Test Fallacies June 19, 2008 by Dave Etchells

http://www.slrgear.com/articles/focus/focus.htm The Goal: Test the Lens and Only the Lens

It should come as no surprise that the expanding interest in lens performance generated by the digital SLR explosion has resulted in much greater testing and review of SLR lenses by various organizations. Unfortunately, as far as we can determine from published accounts of various testing methodologies, a lot of the test data being posted is of suspect value, for a very simple reason: Inadequate control of focus. The purpose of this article is to call attention to this issue, and hopefully to encourage current and would-be lens testers to adopt more rigorous procedures that properly control for focus.