Mirror Since the image in the mirror cannot be projected on a screen, such an image is called virtual image. An image, which can be projected on a screen, is called real image. The image in the mirror (mirror image) is symmetric in the right- and leftwards, but is not in the up- and downwards.
	Concave Mirror A concave mirror with a smooth surface collects incident parallel rays into a focus. Cocave mirror Optical axis, focus, focal length Mirror formula
	Convex Mirror A convex mirror with a smooth surface diverges incident parallel rays. Convex mirror Optical axis, focus, focal length Mirror formula
(1999-2001 Photo by J. Fukue)

	Convex Lens A convex lens with a smooth surface collects incident parallel rays into a focus. Convex lens Cylindrical lens Optical axis, focus, focal length Lens formula
	Concave Lens A concave lens with a smooth surface diverges incident parallel rays. Concave lens Optical axis, focus, focal length Lens formula
	Gravitational Lens Gravitational lens is a phenomena, where rays of light from distant objects are bent by the gravitational field of the intervening object and make images at the observer's site. The gravitational lens is a result of Einstein's general relativity. We can design an optical lens equivalent with a gravitational lens, which has a form like the stem of a wine glass. Such an equivalent glass lens bends parallel rays to produce a double image or a ring image. Lens appearance Parallel rays Double image Quadruple image Ring image ‘F-BASIC program (Windows{Internet Explorer) Try to make a gravitational lens image for various parameters. Easy gravitational lens
(Photo by J. Fukue)