Some ATMers on CN are planning to make fast sub-f/4 Newtonians to hyperbolic. Eg Chantepierre 8 inch f3.5 he is aiming 203mm f/3.5, cc -1.32, fl: 720+/-4mm Tommm planning on a 8 inch f3.7 with cc -1.305 Same time they are waiting Ed Jones to calculate for them the expected conic constant, ie cc At first sight, it seems they are using some unknown formula Later on, it's found they are actually referring to this earlier post: Hyperbolic primary w baader coma corrector from Ed Jones Mike provides a very useful chart to pair with Rosin corrector in this other post Refiguring a 10 in parabolic newton to hyperbolic Davidc135 in this post : The primary's hyperboloid figure must provide to balance the known under-correction of the Baader MPCC III , which will be equal to; 0.81 x (4/f#)^4 So, at f4 the conic of an 8'' primary needs to be around -1.29 to produce 0.81 waves but at f3 the 0.81 becomes 2.56 waves SA and the req...