The 5 mm thick L profiles have been roughly cut to fit the circular shape, they already had exactly the good length. 

2 holes that hold the lens are going to pass thru the 3 mm board and the 5 mm L profile on each side, 8 mm thickness should be good enough to hold the beast in place.

The 2 mm thick 3 cm square tube was bought on a garage sale, it's not as good quality as the other aluminium (the sidewalk high quality), but it will harden the assembly and will be convenient for the design of the hole thing.