[davidmanze]

 Hi Chris ,

                thanks for your input, I am raising the subject because I'm frankly surprised at fact that these telescope lenses produce such sharp images from such simple construction and seemingly so little is known about them. From the practical standpoint,as you say they are very limited by their long and unwieldy dimensions but given that Pentax brought out an equally long and unwieldy lens for 7,000 euros with only 3/4 of a stop more and AF  to better them, it seems that telescope lenses can have their place amongst those who do serious birding on a more reasonable budget.