B00OU9CJ5Q Opteka 500-1000mm f/8 HD Preset Telephoto Lens with Microfiber Cleaning Cloth for Pentax K-1, K-3 II, KP, K-70, K-S2, K-S1, K-500, K-50, K-30, K-7, K-5, K-3, K20D, K100D and K10D Digital SLR Cameras

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HD, super multicoated glass optics with anti-reflection coating for the sharper images
Manual focus, digitally-optimized telephoto zoom lens
Great for the wildlife or nature photographer who wants to be hidden while taking photos of the subject
Gives you the equivalent of looking through a pair of 20x power binoculars
4 Elements in 4 groups