Class 003 principles of light
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Todays lecture of Amit Sir
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Class 003 principles of light
- 1. Principles of Light A Lecture By: AMIT CHAWLA
- 4. Reflection When the reflecting surface is smooth and polished, the reflection is orderly, or specular. Specular light is reflected at the same angle to the surface as the light incident to the surface When the object surface is not smooth and polished but irregular, light is reflected irregularly or diffused ; i.e. the light is reflected in more than one direction. Practically all surfaces reflect both specular and diffused light
- 5. Refraction | Absorption REFRACTION The change of direction that occurs when a ray of light passes from one transparent substance into another substance of different density is called refraction. ABSORPTION When light strikes a medium and is neither reflected nor transmitted (passed on), it is said to be absorbed.
- 10. But how do we see things? The rays of light, controlled by the IRIS , enter our eyes and hit the LENS present in the eye. The lens converges the light which falls on the retina . These rays then excite the nerves (Cones and Rods), which carry message to the brain through optic nerve.
- 12. Other Hidden Things Focus Just like a camera, our eyes also need to focus. Ever tried this exercise? inside our eyes This process is performed by the lens tissues. In cameras this is done by Optical Lenses.
- 13. Other Hidden Things Time of Exposure Most of us have this belief that our eyes see continuous motion. NO! This is Untrue. Eyes capture only a frame at a time just like a photograph. But when we see successive frames, we perceive motion. Cameras capture light by fast action of opening and closing of a shutter.
Editor's Notes
- Before we begin our discussion on “Photography Fundamentals”, I assume that you have taken a photograph at least once in your lifetime; be it with a basic digital camera, or a conventional film camera. But have you ever thought, before or after taking a still picture that what makes you freeze a moment of time? What is that basic element with the help of which (leaving apart the technical, chemical or artistic part of it) you are able to capture a frame? Well answer to these questions is close to the concept of human vision i.e. How humans see things…
- The fundamental element behind photography is “LIGHT”. Light is the RAW MATERIAL not only of photography, but the sight of any living creature. After all, you cannot see or photograph any object without presence of light. Therefore Light is the Fundamental of Photography. There are four basic elements/features of light which all occur at same time. These are:- Light travels in Straight Line (within common substance of uniform composition) until obstructed. You can notice this feature in the Light Beams and shafts of sunlight. Light travels at a great speed (3,00,000 Km/Sec or 186,000 Miles/sec through vacuum). It is inversely dependent on medium’s density. Therefore the speed of Light is marginally slower in Air and still slightly slower in denser substances like water and glass) Light moves like waves; like ripples in water. Different wavelengths gives us sensation of different colours. Light contains energy particles called Photons.
- As we discussed a little earlier, Light travels in straight until obstructed. This happens only if the light is travelling throughout within a common substance of uniform composition. When light strikes surface of another substance, what happens next depends upon the type of material, its texture & colour, and the angle and colour content of the light itself. Broadly three cases are possible when it hits a surface. Reflection : The reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface. The angle between the surface normal and the reflected ray is known as the angle of reflection. The Law of Reflection says that for a specular (non-scattering) surface, the angle of reflection always equals the angle of incidence. Refraction: The refracted ray or transmitted ray corresponding to a given incident ray represents the light that is transmitted through the surface. The angle between this ray and the normal is known as the angle of refraction, Absorption: In physics, absorption of electromagnetic radiation is the process by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other form of energy, for example, to heat. The absorption of light during wave propagation is often called attenuation.
- REFLECTION When light is reflected, it acts in a certain way. When the reflecting surface is smooth and polished, the reflection is orderly, or specular. Specular light is reflected at the same angle to the surface as the light incident to the surface; that is, the path of the light reflected from the surface forms an angle exactly equal to the one formed by its path in reaching the surface. Thus the angle of reflection is equal to the angle of incidence, which is a characteristic of specular light (view A). However, when the object surface is not smooth and polished but irregular, light is reflected irregularly or diffused (view B); that is, the light is reflected in more than one direction. Practically all surfaces reflect both specular and diffused light; smooth surfaces reflect more specular light, and rough surfaces more diffused light. Since diffused light is more common than specular light, it is of greatest value in photography. Objects that are not light sources are visible and therefore photographic
- REFRACTION The change of direction that occurs when a ray of light passes from one transparent substance into another substance of different density is called refraction. Refraction enables a lens to form an image. Refraction occurs because light travels at different speeds in different transparent substances. The speed of light in each transparent substance is called the index of refraction for that substance; for example, light travels 1.5 times as fast in air as it does in glass, so the index of refraction for glass is about 1.5. ABSORPTION When light strikes a medium and is neither reflected nor transmitted (passed on), it is said to be absorbed. Black cloth, for instance, absorb more light than objects such as a white sheet. When light comes in contact with the surface of an object, a mix of reflection, and some absorption takes place. A medium that does not allow light to pass through it is opaque . An opaque material may also reflect light . When an object is opaque and the light is not reflected, it is absorbed by the object. When light is absorbed, its energy is converted and it no longer exists as light. The color of an object is determined by the way it absorbs light falling upon it. A woman’s dress appears red when it absorbs the blue and green rays of white light and reflects the red waves.
- DIFFRACTION DIFFRACTION, or change of direction, always follows a simple rule. “In passing from one transparent substance into another of greater density, refraction is toward the normal. In passing from one transparent substance into another of lesser density, refraction is away from the normal.” In this rule the normal is defined as a line perpendicular (90°) to the surface between the mediums. DISPERSION The speed of light in a medium depends on the wavelength of the light. As light enters a more dense medium, the short waves, such as blue, are slowed more than the long waves, such as red. Thus the index of refraction of a medium varies with the wavelength, and the different colors of light are bent different amounts. This changing index of refraction or the breaking up of white light into its component colors is called dispersion.
- Wavelength is the distance from the crest of one wave to the crest of the next wave. In wave motion theory, light, wavelength, speed, and frequency are important characteristics, and they are interrelated. The wavelengths of light are so small that they are measured in nanometers (nm). A nanometer is equal to one millionth of a millimeter. Wavelengths of light range from about 400nm to 700nm in length and travel in a straight-line path. In other words eyes are only sensitive to a narrow band between wavelengths 400nm – 700nm (1 Nanometer or nm = 1/1,000,000 millimeter). This limited span of wavelengths is therefore known as visible spectrum.
- The rays of light enter our eyes and hit the lens present in the eye. The lens converges the light which falls on the retina. These rays then excite the nerves (Cones and Rods), which carry message to the brain through optic nerve. The brain then understands what the eye is trying to tell and sees the object that the eye was looking at. Similarly, we can see different colors, darkness and brightness. By varying the intensity of rays that fall on the eye, we can make out the different colors.
- Working of a camera is based on the concept of human vision itself. If you have noticed just like your eye all cameras would have a lens, an iris (called aperture in cameras) and a recording material.