Kodak 560 - Manual (Page 19)

6. When you have accomplished the centering of the cone of light on
the screen, install a slide frame (without film or glass). Readjust the
screws so that the cone of light fills the slide area with no hot spots
and so there is no bluish coloring or fringes at the slide area edges.
7. Reinstall the rubber plugs in the adjusting holes for optimum
protection.
Adjusting the Lamp Position
17