F-number lengths. Therefore, reduced–depth-of-field effects will require smaller f-numbers when using small-format cameras than when using larger-format cameras. Image sharpness is related to f/number through two different optical effects: aberration, due to imperfect lens design, and diffraction which is due to the wave nature of light. The blur optimal f-stop varies with the lens design. For modern standard lenses having 6 or 7 elements, the sharpest image is often obtained around 5.6–8, while for older standard lenses having only 4 elements (Tessar formula) stopping to 11 will give the sharpest image. The larger number of elements in modern lenses allow the
Opposite (semantics) has no word that stands in opposition to it (hence the unanswerability of "What is the opposite of platypus?"). Other words are opposable but have an accidental gap in a given language's lexicon. For example, the word "devout" lacks a lexical opposite, but it is fairly easy to conceptualize a parameter of devoutness where "devout" lies at the positive pole with a missing member at the negative pole. Opposites of such words can nevertheless sometimes be formed with the prefixes "un-" or "non-", with varying degrees of naturalness. For example, the word "undevout" appears in Webster's dictionary of 1828, while