CameralandNY has fixed power Pentax eyepieces on sale most of the time. 2 fixed cost about the same as one Pentax variable. My variable eyepiece is as good as my vision can tell (I wear eyeglasses, so European scopes are kind of wasted because of the extra glass-air interfaces) until it's completely maxed out. Then even I can see the image degrade. Just like my Pentax 55-300mm camera lens.
