I love this photo for its candidness. Unbelievably clear and real. On the back is a postcard written from Oscar. The translation comes from my grandfather:

My dear Parents, my best thanks for today’s postcard. After I worked very hard all day drawing, I recuperated for a short while in the Cafe. When will you, dear father, come visit here. From Manfred (Oscar’s Brother) I received a card the other day. Best wishes from your devoted son, Oscar. 

I really wonder what oscar was “drawing”. Maps? Army plans? Clearly he felt safe enough to invite his father up to Hamburg.