So I wanted to make a simple spectroscope for my kid that teaches astronomy. Many of the simple ones made with toilet paper tubes look king of kludgy and have the distraction of the direct light shining through the slit. Also, the spectrum is off to the side and not directly centered in the eyepiece. So I oriented the viewing aperture so that the spectrum was centered in the grating and the direct light from the slit was blocked. For good measure, I added baffles to reduce light bouncing.