> As an extreme example, if your aperture is a single point (a pinhole camera), the image can be focused without a lens. Diffraction limits the sharpness, thou

> As an extreme example, if your aperture is a single point (a pinhole camera), the image can be focused without a lens. Diffraction limits the sharpness, though. https://en.wikipedia.org/wiki/Diffraction-limited_system https://en.wikipedia.org/wiki/Diffraction-limited_system. Pesky wave nature of light in action. > Articles describing this seems to say it's caused by the film medium, rather than being an optical effect. Halation in film is caused by reflection from the back of the film. Most of them have an anti-halation layer to reduce this effect. I don't see any reason why one's eye wouldn't also be vulnerable to this effect (and probably has some biological mechanism to prevent light from being reflected out of the eye. Cats sure don't have this, though.)