Thanks Guys. I will try the milk jug fix for the Azmimuth motion of the Dob. <br /><br />I am most intriqued by the answer to my first question, and I've been wrestling with that answer for a couple of days. This is really quite a profound answer. <br /><br />I guess the reason is that "Exit Pupil" is actually a measure of the efficiency which our eye and the EP work together. Since the average adult dialated retina is approximately 6.5 to 7mm diameter, anything much over this diminishes available light to our cones and rods. Anything much under this admits all the light, but doesn't take advantage of all the cones and rods available, diminishing contrast, resolution etc.. <br /><br />My understanding of telescope and eye piece "Exit Pupil" is very fundamental. However. it is defined ExPu=EP focal length / Telescope focal ratio. Thus the "Exit Pupil" is not just a function of the telescope exclusively or the eye piece exclusively, but both combined. Which I think is quite profound. <br /><br />The reason I am intriqued by the answer to question one, if that answer is true, this definition of "Exit Pupil" appears to be more complex then my understanding is. <br /><br />For Example. If my telescope has a focal length of 1200 mm, focal ratio of f/f.4 ( apature = 254mm ) and an eye piece focal length of 32 mm, I arrive at a very efficient and bright image "exit pupil" of: ExPu=(32/(1200/254)) = 6.77 mm. Almost exactly the right exit pupil for maximum efficiency of viewing all of the available light. If I add a barlow 2x and double the magnification, it would be great if I could maintain the maximum efficiency. However, if a barlow doubles the focal length of the telescope, then according to this calculation:<br />ExPu = (32/(2400/254)) = 3.386 . Which is what I would expect, but not really want. So if the "Exit Pupil" does in fact remain constant, then something is missing from this relationship. and my understanding of it ??? Which is why intrigued by it