What is the Total Internal Reflection of Light Use
2: The working of binoculars.
Binoculars need to increase the separation of the collectors, so that far-away objects can still be seen stereoscopically. Prism binoculars rely on TIR so that they don’t have to use reflective coatings to achieve the reflections needed to narrow the separation to that of your eyes.
It is a common misconception that rainbows are caused by TIR. Not only is that false, TIR is physically impossible inside the spherical raindrops that produce rainbows. By definition, the light enters the drop at less than the critical angle. The path of the light inside the drop forms an isosceles triangle with the surface normals (radii) of the drop, so the angle when it reflects is always less than the critical angle.