I know that a lot of guys in the bird and astro forums have used the 8-24mm Vixen Lanthanum zoom. It is brighter than the XF Zoom with more eye relief also. Well, now it appears they have come out with a new wide angle model. I don't know anything about it but it might be worth checking out. I know the first ones have no prob reaching full focus on the Pentax spotters. The price is about what I paid for my William Optics zoom. I think one of you guys should buy one from an outfit that will allow you a 30 day return, check it out, and tell us how it works!! The 8-24mm zoom will give 16-48X on the PF 65 scope. The scope has a focal length of 390mm. 390 divided by the focal length(s) of the eyepiece give the magnification. The WO zoom is 7.5-22.5mm. Which gives about 17-52x.