"but if you lose the ability to make a proper lens,"
It is difficult to see lenses becoming obsolete - unless cornea manipulation gives everyone 20/20 vision.
Lenses have been in use since the time of Galileo. Silver based photography was an invention of the late 19th century. The more primitive a technology - the easier it is to reproduce later - especially if the way to do it is documented.
Technology is a pyramid of gradual improvements in techniques and materials. Lose some of the intermediate steps and you are back to a more primitive society. One of Philip K Dick's stories was based on a post-apocalyptic society - where landfill sites were mined for discard equipment's transistors.
Biting the hand that feeds IT
