Pentax has unveiled its new DA 18-270mm F3.5-5.6 ED SDM lens.  The 15x zoom lens covers a 27.5-414mm equivalent on Pentax's crop sensor bodies like the new Pentax K-5 II.  The new 18-270mm lens features Pentax's SDM AF system with a supersonic motor for faster AF speeds, along with two extra-low…