The loss of brightness limits the use of lenses with a working aperture of f / 2.8. As written by other reviewers eimem, a lens with aperture 4 under good lighting conditions is possible here, but I would rather resort to the other focusing screens.
In order to change the disc you just need a little skill and a fairly dust-free environment. Should be avoided in any case, attempts to clean the writing itself without the right equipment. The matte screen is for that matter is very sensitive and reckless attempts verschlimmbessern the situation at most.
