A lens is a kind of hole (opening) that concentrates light to create an image. Light is also diffracted when it passes through a lens. The diameter of the diffraction spot increases with longer wavelengths light and holes with smaller diameters. With a microscope or telescope, diffraction greatly influences resolution because the object lens diameter is essentially a hole. Diffraction has a major impact on resolution because a smaller opening causes an image to fade. In other words, even with an ideally designed lens, light will become fuzzy even when in focus, since the light is not focused on a single point.

This is called the "diffraction limit of the lens. " To magnify something like a molecule using a lens, you need an object lens with a very large diameter. It is almost impossible to create such a lens, which is why scientists use electron microscopes incorporating electron beams whose wavelengths are smaller than those of light. These devices, using shorter wavelength beams, reduce the size of the diffraction image and provide high resolution.