Bernie Gunther's Leica IIIa
One of my favorite series of detective novels are the Bernie Gunther stories written by Philip Kerr. Bernie is a policeman in Berlin and the central character in these film noir-like novels. In the early novels he's solving murders while coming to grips with the rise of the Nazis whom he absolutely loathes in pre-war Germany. Mid-series novels have him actually conscripted into the SS that he hates so much because the SS absorbed the Berlin criminal police deprtment. Later novels have him living in Argentina or France dealing with the aftermath of the war, but feature flashbacks to earlier cases not previously described. A great series that I heartily recommend, although I'm saddened to hear that Philip Kerr died in 2018.
The third to last novel he wrote is called Prussian Blue. A portion of it covers a case he investigates in 1939. On page 79 he demands the tools he'll need to investigate the case including "a Leica IIIa with a 50mm F2 retractable Summar lens." When I read this, I glanced over to my shelf of vintage cameras to gaze adoringly at exactly this camera/lens combo.
By looking up the serial number, you can tell that my Leica IIIa was made in 1936. So it could have been Bernie's camera (if he weren't a fictional character).
The Summar lens is from the same time period. It had some haze in it when I got it which really lowered the contrast, but I took the lens elements out and cleaned them with alcohol which helped tremendously (see blog post on this).
With the Summar lens, collapsed, the IIIa is highly jacket-pocketable and can take great pictures as seen below. Going to f/2 means you can use it for indoor and night shots. This is probably my favorite camera to shoot. It's a real jewel. The Leica IIIs are the pinnacle of Oscar Barnack's inventiveness at Leica.