What is the difference between f-ratio, focal length and focal point?
Good Question! I think these were designed for confusion. Focal point is the actually spot your telescope brings light to a point. Focal length is the distance between the optics and the focal point. In the case of a refractor it is generally the length of the tube. For a reflector, focal length is the entire length light travels, bouncing off all those mirrors. Focal ratio or f/ is the ratio between the focal length an the aperature. A 10 inch f/4.5 scope has focal length of 45 inches of roughly 1125 mm.
