Images Above - Leica M7 Voigtlander 10mm f5.6 VM Hyper Wide Heliar Lens, Agfa ISO 200 Colour Negative Film.
The wild wacky and wonderful Voigtlander 10mm f5.6 VM Hyper Wide Heliar Lens. Using this lens you have to be very careful not to include yourself in the frame. It's VERY wide. For APS-C you would need a 6.6mm lens for this angle of view. For m4/3 a 5mm. It's small, thanks to it's f/5.6 minimum aperture and not too heavy at 375g, but it's not cheap. But it has this great advantage. If you set it f/11 (or f/8 at a push) you don't actually have to focus it. Because at that aperture everything is in focus from it's minimum focusing distance (30cm / 11.8") to infinity. So it's good for 'shoot and run' street photography. However I use for considered landscape / location work and house interiors on a tripod.
The image quality is superb, it's very sharp with only a slight fall off in the corners and it's buit like a tank. You can get it with native mounts for Sony e-mount or use it on any other mirrorless camera via an adapter. On APS-C it's a 15mm equivalent. Still seriously wide. One of my favourite ever lenses.