I have owned the 10x50 Pentax's in each version, the SP & ED. Vortex makes a fine product but having never actually using their Viper HD 10x50 & seeing their eye relief spec's, these would not work for me. If I were to need another 10x50 binocular for close up detail & did not want to spend a lot of money, I would purchase another Pentax just because of the big difference in the eye relief. The small difference in FOV between the two is another reason why I would not purchase the Viper over the Pentax. Pentax's have very comfortable long eye relief of 22mm compared to the Viper & I saw no blackout problem. The Pentax is very user friendly & optically is very nice. Since CA is not a problem for me, I would purchase either version , the SP or ED. Also the Pentax ED has a more quality look & feel than any Viper I have owned. ... gwen