Ruth Craft, former director of the planetarium at Kennedy Primary Academy in South Bend, IN, designed a simple means to show how lenses affect the light path in a telescope. Hand-held lasers will emit bright light that remains well-defined as it travels through a dish filled with Knox® gelatin. By swapping out different lenses between the lasers and the dish, one can cause the light to converge at different focal lengths. Some of the lenses she fashioned from gelatin itself, which she smoothed with a hot knife.
In a variation, Craft filled half of a Galileoscope with gelatin to illustrate how the main optical lens bends incoming light so it converges at the eyepiece.
Craft debuted her unique exhibit at SBCSC's AstroFest in May 2014. One visitor even moved his tri-focal eyeglasses through the lasers' light path to create multiple results. She repeated the demonstration at an observing event on behalf of Michiana Astronomical Society Inc. at St. Patrick's Park later that month, and put a concave mirror at the opposite end of the dish to illustrate the properties of a reflector telescope.
Thanks, Ruth, for the innovative demonstration.
Slideshow shows the outcome when different lenses are placed between the red lasers and the dish of gelatin.