The 7 Artisans 18mm F6.3 is a very special lens belonging to the category of lens cap lens : so tiny that it as tiny as a lens cap. In total it is 10mm thick , so much thinner than a pancake lens !
With this design with have a fixed aperture of F6.3 and no focusing ring the lens is more or less focused at the hyperfocal distance (=2.53m at 18mm F6.3) , with theoretically everything in focus from 1.29m to infinity. In practice everything will be sharp from 3-4m to infinity but the closer the subject the more blurry it will be. So to be used for distant subject.