We hope to clean up some more stray light within the system by masking off shiny parts of M2 & M3 that do not form part of the mirrors' clear apertures. The aperture stops are made of a non-reflective black material & those at the outer edges of the mirrors are attached via the SAC cage.
The M2 stop is the black ring just below the mirror in the next two images. It is seen here from inside the SAC while M3 was out of the way.
& here it's viewed from below through the hole in M3.
M3 also has a similar ring just above its surface, seen here from underneath - blocking the gap between M3 (left) & the SAC cage (right).
The aperture stop for the inner part of M3 had to be attached directly to the optical surface.