While talking to a fellow interested in imaging yesterday, this question came up: Would the image be identical if taken through 8-inch & 12-inch telescopes if they were both f/10? The answer is no. F/10 in an 8-inch scope equals an 80-inch focal length. In the 12-inch, the same f/ratio yields a 120-inch focal length. Clearly, the image scale (magnification) will be much greater on the larger telescope. If the 12-inch were an f/6.666, then the image scales would be identical. Image size is always determined by focal length; whatever the f/ratio happens to be is irrellevant to magnification. Chuck __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com