A box camera is a simple type of camera, the most common form being a cardboard or plastic box with a lens in one end and film at the other. They were sold in large numbers during the late 19th and early 20th centuries. The lenses are often single element designs meniscus fixed focus lens, or in better quality box cameras a doublet lens with minimal (if any) possible adjustments to the aperture or shutter speeds. Because of the inability to adjust focus, the small lens aperture and the low sensitivity of the sensitive materials available, these cameras work best in brightly lit day-lit scenes when the subject is within the hyperfocal distance for the lens and of subjects that move little during the exposure. Eventually, box cameras with photographic flash, shutter and aperture adjustment were introduced, allowing indoor photos.