How to choose a camera lens

In the words of Scott Bourne, a professional photographer, author, teacher and pioneer in the digital imaging field ... First, you should know the criteria for choosing a lens. Some of the criteria are subjective likeIs this lens appropriate for the intended purpose? Is it versatile enough? Do you like the look and feel of the lens? These are important, but hard to measure criteria.You should also consider more measurable criteria, such as: Lens sharpnessLens speed (F/2.8 is a faster lens than F/5.6 and faster is usually better)Minimum focus distanceNumber and type of lens elementsManufacture for film, digital or both (Lenses made specifically for digital cameras will often not work properly on film cameras)Amount of lens flareAmount of chromatic aberrationBokeh (How the out of focus background appears)Light fall off (Corner to corner illumination)Lens weightLens construction and build standardsLens focus speedStabilizationErgonomicsPrice Lets take a look at each of these criteria, and where possible, how you should test them: 1.