Question

5.What would happen if we dont consider rays as paraxial.

Answer 1

Actually the formulas derived for the calculation are when the rays are paraxial i.e. A paraxial ray is a ray which makes a small angle (θ) to the principle axis of the system, and lies close to the axis throughout the system.

It reduces the calculations and makes the formulas easy!

Like we are able to take the approximations like
sinθ = θ
and carry on our calculations
where θ is the angle between incident ray and normal.