1. The Chinese Future Giant Telescope has a primary focal ratio of 1.2. 2. :It's not the absolute diameter that matters, but the focal ratio or f-number. 3. It uses a concave focal ratios , Dall-Kirkhams are seldom faster than f / 15. 4. The particular aberrations associated with the coma ) are also worsened with short focal ratios . 5. Also, for fast focal ratios , the curve obtained is not sufficiently exact and requires additional hand correction. 6. Early off-axis designs such as the astigmatism and long focal ratios , which make them useless for research. 7. The " focal length " of the telescope objective is the diameter of the objective times the focal ratio . 8. Many of these targets are small and require long focal lengths, which can push the focal ratio far above 5. 9. The focal length of 12.1 m combines with the baffled aperture of 3.7 m to a focal ratio of 3.26. 10. A secondary mirror is to produce an unobstructed field-of-view of 20 arcminutes in diameter with a focal ratio of 15.
