I was asked the question about how to position baffles in a refractor, I got my info from a booklet I bought in a magazine store in the late sixties called Exploring Space with Astronomy by Lloyd Mallan, pub. by Fawcett Books, it describes how to build the imfamous Jaegers 5" RFT, If you want to place baffles in a 6"F15 refractor you first must draw a full scale drawing of the cone of light, I used my kitchen table for my scope, you draw a line 90" long for the focal length, at one end draw a vertical line 6" for the objective at the other end draw a vertical line for the image size at the focal plane you then draw the outer lines to make a full scale drawing of the light cone, and from that you can accuratly locate the baffles, you determine the image size with your lowest power eyepiece, for example a 50mm eyepiece would be 45x and you multiply the focal lenght of the objective 90" by the factor .015 to get an image size of 1.35", the factor to determine image size come from a book once published by Edmund Scientific called "Home Built Telescopes"...Bob.