The Afterschool Universe (AU) program, sponsored by the Goddard Astrophysics Science Division Education and Public Outreach program, produces educational materials for afterschool enrichment programs.
During 2010 the group started putting together a series of tutorial videos, produced by the Goddard production studio. One of these covered how to make a "paper towel tube spectroscope." I was requested to help provide photographs of the resulting spectroscope.
Initially, we tried shooting through a paper towel tube, but the diameter of the digital SLR lens was larger than that, and even in a darkened room, it really did not work well.
The three of us (myself and the two AU people, Sara Mitchell and Sarah Eyermann) decided that we could do the same thing with a larger object, so we located a poster mailing tube, 4.5 inches in diameter and 37 inches long.
The resulting images were used in the video shown in the links below. You can even see the grain in the brown cardboard mailing tube as shown through the light falling through the slit!
You can also see this on the Afterschool Universe YouTube channel.