An experienced optical engineer can tell a great deal about a lens by just by looking at the image. A full discussion of this topic could fill a book, but here are some tips.

The classic USAF-1951 target is often used to determine the smallest feature size that can be resolved by a lens. Though still widely used, the test suffers from subjectivity. Different operators may disagree on which feature is "resolved."

PixelScope OpticStudio™ allows numerical measurment of 3-bar contrast, removing the issue of operator subjectivity.