I have been also working on a far more stable entrance slit design and decided to include it with the build instructions. I have tested it several times and will post my results, I made one for my 0.12mm slit and my 0.09mm slit.

The slit I am using now is the 0.09mm one.

http://publiclab.org/notes/dhaffnersr/08-11-2016/complete-redesign-of-entrance-slit

Supply source for blackout material and the aluminum black tape I used:

http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=190 – blackout materials ect.,

T205-1.0 - AT205 Black Aluminum Foil Tape 1" x 81' (25 mm x 25 m) Roll Cost-$28.80 a roll