This is not an enlarger. It is part of a Leica Reprovit, which is used with an M body and a Focotar lens. The Illuminator projects an image through the Focoslide onto the baseboard. The Illuminator is only used for focusing and composition.
When the Focoslide is moved into position with the body over the lens, only then is the exposure is made.
Basically, it was Leitz's elegant copying device. What you would need to complete this outfit is a Focotar lens, a copy stand with a vertical post and copy board, some lighting setup, and an M body.
I used the complete Leitz Reprovit IIa for many years when I made slides and copy negatives for clients.