From one point O, draw three straight lines. Take three points A, B and C. Now Find a point B' on the extended line of OB, with OB' = 5/3 OB or BB' = 2 OB / 3.
Then draw A'B' parallel to AB and draw C'B' parallel to CB, intersecting the first lines that were drawn from O.
Or, Locate B', C' and A' on the initial straight lines such that OB' = 5 OB/3, OC' = 5 OC/3 and OA' = 5 OA/3. Join A',B' and C'.
The point O is the source of light and ABC can be thought of as an opaque object.