Well I used my 3D printer, machine shop and tried to make an approximation of the device suggested here and I get absolutely nothing.

As you can see, I blackened two utility blades and mounted them on top of a 10 mm hole in the distal end. The slit is 0.1 mm wide and of course 10 mm long. I'm not sure if you can see it, but I mounted my DVD grating on a plane, angled 60 degrees to that end cap with the slit. I then made a tube that, at it's midpoint takes a 45 degree turn to the ocular end, i did not target any particular lengths in either tube as i only caught some of those suggested measurements after printing this out. I certainly can trim either tube. I twisted the one tube on the other a full 360 degrees. I am not at all clear on what was meant in the instructions about the grating lining up with the slit or what we are supposed to notice when it does. i cannot remember now which way my grate lines go but as i said, the design allows me to rotate a full circle.

Anyhow, looking in that short 45 degree eye piece end, I don't see anything but my dvd plastic , when I point the slit at a light. The grating is functional, I can see a reflected spectrum when the light, incoming from my face end catches the grating. Not sure what I'm doing wrong but appreciate some critiques or suggestions.