Ask David: Should I purchase an off-brand lens for my camera? - Digital Photo Secrets: "Off brand, or third-party lenses, have both perks and pitfalls. Some photographers will swear by third-party lenses, while others swear they are not as sharp or reliable as a proprietary lens. The first and probably the most important advantage of an off brand lens is the price. Quite often, third-party gear companies make lenses that are similar in capability to those produced by major camera companies at a fraction of the cost, especially when you get into higher end or more specialized lenses."
'via Blog this'