Build Your Own SLA/SLS

I have tried to impose a mask - does not help
uneven illumination occurs on each individual object.
I think the problem is the output lens or electronics compensating illumination on different objects.
I partly solved the problem by addition of a large amount of pigment to resin

Not sure why they have the metal piece on some projectors, others do not have it, so maybe
a way to correct optical errors, was any dirt present?, it looks like a newish device so should not
be as dirty as my ancient units, at least you now fully understand the optic system you have.