Makes me curious what "trained engineer", as you once said you are, means. You have proven, over and over, that fbk was right. The only hint of an engineer you have is that your writing is terrible and that's about it.
Well, if you actually did go to school for an engineering degree, you might have taken one of the material classes, either science of materials, or engineering of materials, maybe I or II - depends on or your area of [lack of] expertise.
Just recall that there are optical properties that your tired little eyes can't see under normal conditions - which doesn't mean they aren't there and will manifest under the right conditions. Remember that you can look, with the right tools, at a seemingly flawless solid block of steel and identify where it will crack under stress. Well, acrylics aren't much different. It's not because you don't see imperfections with bare eyes that they are not there. Beam a light and they start to appear. You once found very funny that I was looking at at light transmission curves for different materials, but maybe you just missed the classes (or all of them during your engineering degree) that talk about standardized testing. Maybe your method of taking a picture on a living room is much more precise.
I don't have own this piece of plastic to tell you how it's made, it just takes knowing how cell-cast acrylic is made and what are the limitations of that method in manufacturing irregular shapes.
It doesn't take a genius the realize that the people that designed this filter do not dive, nor have any UW knowledge You actually got to be very ignorant NOT to realize that - or purely stubborn.
