Hi Kurt, A pen light would give a continuous spectrum (actually a black body distribution) and not show calibration lines. A good source for calibration lines is a neon bulb running on AC current as might be found on many kitchen appliances to indicate that they are on. There are many lines in the red portion and a few dim ones toward the green. As you want the source to be as stellar as possible mounting it a ways away on a nearby wall will reduce the "glow" size. Picking a bright hot star with plenty of emission lines will also serve as a rough calibration. I have many times thought of an objective prism for the telescope ala, Henrietta Leavitt and Anne Jump-Cannon. Jerry Foote ScopeCraft, Inc. 4175 E. Red Cliffs Dr. Kanab, UT 84741 435-216-5450 jfoote@scopecraft.com