The camera obscura or pinhole image is a natural optical phenomenon. The cover images are pinhole polaroid photographs. This phenomenon is known as camera obscura or pinhole image. Among her tools are pinhole cameras and Polaroid cameras. The oldest "lenses", pinholes, used in pinhole cameras, keep perspective accurately. The pinhole optic for Lensbaby creative lenses has an aperture of just 177. A cylindrical oatmeal container may be made into a pinhole camera. Epipolar geometry of this sensor is quite different from that of pinhole projection cameras. A pinhole camera effect can sometimes occur naturally. The description above corresponds to the pinhole camera simplified optics classically used in computer graphics. The geometry related to the mapping of a pinhole camera is illustrated in the figure. Due to the large f-number of a pinhole camera, exposures will often encounter reciprocity failure. Even if the image is sharp, it may be distorted compared to ideal pinhole projection. Refractive error can be corrected using a pinhole occluder. The first glass insulators used in large quantities had an unthreaded pinhole.