They have been making SLR lenses for decades. Nikon owners are particularly lucky since the SLR lens made for the Nikon SLR's of the 1950's and 1960's still physically fit on the newest DSLR's (with some compromises). Canon, Sony, Pentax and others are not so lucky. But there are adapters for you to fit almost any lens on almost any modern camera.
This challenge is for photographs from these old lenses. Any subject, any shoot date, any camera. But you have to use an OLD LENS (as defined below).
Couple that old Canon FD lens to your 5D through the adapter; try that old 90mm portrait lens your father bought in 1975; take a picture with a Sony NEX and and a classic Leica lens from eBay; scan in a negative from your school days in the 80s (or 50s!)--use your imagination.