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Hi Bill
When you draw the light cone don't draw it to a point at the eyepiece end of the focal length. Make the eyepiece end of the focal length a line equivalant to the diameter of the fully illuminated field about 27mm for 1.25 inch eyepieces or 46mm for 2 inch eyepieces. Then baffles theoretically should be spaced such that any off axis light ray entering the objective end will not reflect of the tube side and on to the focal plane. You may find it only takes 2 or 3 or 4 baffles to achieve this. When I made my wooden refractors I didn't worry about the spacing too much as the baffles were acting as frames so I just spaced them equally about 200mm apart.
If you can get hold of a copy of Telescope Optics by Rutten and Venrooij (Willman Bell) there is a descrption of the theory in Chapter 19. Also Build your own telescope by Richard Berry (Willman Bell) has a plan for a 6 inch refractor.
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