Two types of lenses for deep underwater photography

In underwater photography, the object is immersed in water while the image is usually formed in air. The most obvious, straightforward way to form an image under these circumstances with a conventional type of lens is to use a plane parallel slab of glass as a window in front of the lens to separate the water from the air space. For most types of camera lenses, this is a perfectly adequate solution; But if one looks at the problem carefully, it is evident that such a system introduces a chromatic aberration referred to as lateral color. The source of this aberration is illustrated in Fig. 1. The dispersion at the glass to air interface overcompensates for the dispersion at the water to glass interface. As a result, the direction of a ray entering the camera lens for any given ray incident on the window varies with the wavelength of light.