・R_1 * sin θ_1 = R_2 * sin θ_2
・R_2 * cos θ_2 = R_3 * cos θ_3
・θ_1 = θ_3 < θ_2 , R_1 > R_2 > R_3
Based on this assumption, the following formula was found.
・R_2 / R_3 =(R_2 / R_1) * (tan θ_2 / tan θ_1)
=(sin θ_1 / sin θ_2) * (tan θ_2 / tan θ_1)
・R_2 / R_1 =(R_2 / R_3) * (cot θ_2 / cot θ_3)
=(cos θ_3 / cos θ_2) * (cot θ_2 / cot θ_3)
=(cos θ_3 / cos θ_2) / (tan θ_2 / tan θ_3)
circle ratio / chord ratio= R_2 / R_1
I do not know well that viewspeed is combined at this ratio...