Hello Mark, For any reasonable size refractor - say 4" aperture or 5" aperture, I think that maybe 3 or 4 baffles are all that is required. I would put them roughly equally spaced along the length of the telescope tube. A good way to understand the arrangement is simply to draw the whole thing out full size,on a large piece of paper (wallpaper works well). The diameters of the baffles can be calculated easily or just take them from your drawing,directly. If you imagine lines drawn from the outer edge of the objective lens, to the outer edge of the largest eyepiece you want to use , then that should work. To check that the baffles are not too small- look through the telescope from the objective end. It must be possible to see every part of the eyepiece lens from every part of the object glass. If in doubt, let me have the details of your system and I will sort out the dimensions for you. I have made many refractors and I usually make the baffles out of wood or thin aluminium. Are you making your own lens? Let me know if I can help. My E.Mail is soc@onyxnet.co.uk Best of luck with your project. Regards, David. (England)