The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Reflection of Light                             Refraction of Light
lighting up the shadowed side of a sitter's face ; but care should be taken, however, that too much reflected light is not used, or the result will be a hard and lifeless picture. Mirrors should rarely be used, and a rough, not too white surface is the best.
Reflection Of Light. When a ray of light falls upon a mirror, the ray is bent from its original direction into another ;
this is said to be reflection. Reflection of light obeys certain well-known laws, the first of which is that the reflected ray must lie in the same plane as the incident ray ; the second law is that the angle formed by the reflected ray with the normal must be equal to the angle formed by the incident ray. The reflected ray, CE, is in the same plane as the incident ray, DC, and the angle ecf is equal to the angle dcf (fig. 109).
Refraction of Light. When a ray of light passes obliquely from one transparent medium to another it suffers refraction, or is bent out of its course on emerging from that medium. Re-fraction obeys well-known laws somewhat similar to reflection. The first law is that the incident, the normal and the refracted rays are in the same plane, and the second that the sine of angle formed by the incident ray with the normal bears a constant ratio to the sine of angle formed by the refracted ray with the normal. The sine of the angle of refraction, in relation to the sine of the incident angle = 1, is the refractive index of the substance. It is necessary for practical opticians to find the refractive index of their glass, and this they do often by making it into a lens of known surfaces, and finding by trial the focus of the lens. It can also be done by decomposing a ray of white