Similar problems are associated with the pinhole optics of the camera obscura, a camera that forms an image of a scene by projecting light from the scene through a pinhole. A rule of thumb states that a good balance between illumination and resolution is obtained when the diameter of the pinhole is about 100 times smaller than the distance between the pinhole and the image screen, effectively making the pinhole an f/100 lens.
Optimum, however, is not necessarily good. The level of illumination on the image screen projected from an f/100 pinhole would be more than 1,000 times dimmer than that from a standard f/2.8 camera lens. Perhaps worse, the resolution of the pinhole lens cannot be smaller than the diameter of the hole. The resolution of an f/100 pinhole is about half a degree, making the camera obscura barely able to notice that the Moon looks like a disk rather than a point of light. However, an f/100 glass lens with a diameter of an inch can see lunar craters smaller than 10 miles (16 km) across.
The potential for dramatically improving the performance of pinhole-based neutron optics led the MIT Nuclear Reactor Laboratory group to develop an imaging neutron microscope. Their goals were to increase both the resolution of the image and the level of illumination, so that the neutron microscope can quickly produce higher-quality images. Unlike the case of an optical microscope, however, there is no equivalent of optical glass from which lenses for neutrons can be made. Conventional mirrors also tend not to work, as the neutrons simply go through them.