On the axis of parabola  $y^2=8x$ ,there is a point $P(4,0)$ .
A chord $L_1$  making an angle ${\theta }_1$ with the positive direction of x-axis through $P$  meets the parabola at $A_1$  and $B_1$ , and 

a chord $L_2$  making an angle ${\theta }_2$ with the positive direction of x-axis through $P$  meets the parabola at $A_2$  and $B_2$ , and 
 a chord $L_3$  making an angle ${\theta }_3$ with the positive direction of x-axis  through  $P$ meets the parabola at  $A_3$  and $B_3$ , and
 also a chord  $L_4$ making an angle ${\theta }_4$ with the positive direction of x-axis  through $P$  meets the parabola at $A_4$  and  $B_4$,  $(0<{\theta }_1<{\theta }_2<{\theta }_3<{\theta }_4<\frac{\pi }{2})$
then the value of 
$\frac{1}{{\left(A_{1}P\right)}^2}+\frac{1}{{\left(B_{1}P\right)}^2}$ + $\frac{1}{{\left(A_{2}P\right)}^2}+\frac{1}{{\left(B_{2}P\right)}^2}$ + $\frac{1}{{\left(A_{3}P\right)}^2}+\frac{1}{{\left(B_{3}P\right)}^2}$+ $\frac{1}{{\left(A_{4}P\right)}^2}+\frac{1}{{\left(B_{4}P\right)}^2}$ is _______