how can i implement Constant border in material?

i want to same material about camera viewing.
also, i intend to implement constant border with two color(white and blue) for sphere.

so, i used fresnel for material.

and it looks like well when camera is far away from this sphere,


but when camera getting closer it looks different from what i intended
Specifically, The blue boundary is larger than the white boundary. but i want to get constant width border.

what should i do for solving this problem? thanks to read my question.