When choosing a lens, performance is key. Part of that performance is how well it holds up over time. A big part of longevity is its durability. There are a few questions to cover whenever evaluating the build quality of a lens. The first is, does it have weather sealing rings? Weather sealing will keep out the elements of the the world. From dust to moisture, environmental contaminates will destroy the lens mechanics, shortening its life, or killing it completely. Second, what material is it made of? Although plastic’s have evolved and improved over the years, the tried and true build material is metal. Typically, the more affordable the lens, the cheaper the building materials are. A material like plastic, although great when other options aren't available, isn't as robust, strong or last as long as a lens built of metal. Third, does it have an internal or external zoom mechanism? It is easy to spot an external zoom mechanism. When operating the throw of the lens, it will telescope out and retract in. External zooms are more prone to environmental contaminants gunking up the movement of their zoom. A more robust design are internally zooming lenses. Their movement is encased in the lens, allowing it to keep its form, and protecting the movements from the elements. Another key element to performance is its usability. A lens’s usability is connected to what options it offers, how well those options function and how they interact with added accessories. Filter thread diameter and how smooth the controls function will qualify a lens’s usability. When assessing a lens, find out what size filter thread it has. It‘s important that the lens have thread at the end of the lens for a filter such as a uv filter or nd filter, as well, the size plays a big role in how expensive those filters might be. And lastly, smooth ring control is a key feature, because most affordable lenses are designed for photos, how smooth the focus ring functions, as well as how fluid the zoom ring works will make a huge difference in its usability when shooting video. Making sure you put your money into the lens that meets your needs and will stand the test of use over time will insure a good investment.