Old optic problems
https://community.ptc.com/t5/PTC-Mathcad/What-is-not-correct-in-this-optic-problem/td-p/287167
https://community.ptc.com/t5/PTC-Mathcad/Parabola-Mirror-an-error/td-p/365093
https://community.ptc.com/t5/PTC-Mathcad/A-spherical-lens-where-is-a-focus/m-p/161402#433664
In the past century, many families have lenses with four boundaries between media "air-to-glass (or rather, plexiglas)", "air-to-liquid", "liquid glass" and "glass-to-air." They were placed in front of TV screens which at the time was little more than a postcard. Also fills the lens with distilled water, and better - glycerine whose refractive index higher.
Luc and all, wath is the best form for the front surface of this nostalgia-lens? The back surface is the plane.
You can try to read information on the picture:
Price - 900 Ruble (now 12$).
For rich men - Leningrad-TV with radio set (The girl was crying - she did not have enough money for this TV - 2000 Ruble, only for KVN-49):
