Accommodation Model

Being inherently a thick lens problem, image formation by the eye can be approached using a system matrix. By modeling the fixed portion of the eye with a matrix, assuming the front surface of the crystalline lens to be fixed, then the thickness and back surface power of the lens can be varied to study the accommodation process.

By computing the system matrix for the entire imaging process, constraining the image to fall on the retina, the object distance on which the eye is focused can be calculated. (If an image is to be formed, the object distance must be negative since the Cartesian sign convention is used.) Alternatively, by choosing and object distance, the required back surface power can be calculated.

Lloyd's’ mirror experiment

Lloyd's mirror This is another method for finding the wavelength of light by the division of wavefront. Light from a slit So falls on a silvered surface at a very small grazing angle of incidence as shown in the diagram (Figure 1). A virtual image of So is formed at S1. Interference occurs between the direct beam from So to the observer (0) and the reflected beam The zeroth fringe will be black because of the phase change due to reflection at the surface. Application An interesting application of this effect may be observed when a helicopter flies above the sea near a radio transmitter. The helicopter will receive two signals: (a) one signal directly from the transmitter and (b) a second signal after reflection from the sea As the helicopter rises the phase difference between the two signals will alter and the helicopter will pass through regions of maxima and minima. Lloyd's mirror Experiment Lloyd’s Mirror is used to produce two-source interference...

Thin-Lens Equation:Newtonian Form

In the Newtonian form of the lens equation, the distances from the focal length points to the object and image are used rather than the distances from the lens. Newton used the "extrafocal distances" xo and xi in his formulation of the thin lens equation. It is an equivalent treatment, but the Gaussian form will be used in this resource.

Fresnel's Biprism

A Fresnel Biprism is a thin double prism placed base to base and have very small refracting angle ( 0.5o). This is equivalent to a single prism with one of its angle nearly 179° and other two of 0.5o each. The interference is observed by the division of wave front. Monochromatic light through a narrow slit S falls on biprism , which divides it into two components. One of these component is refracted from upper portion of biprism and appears to come from S1 where the other one refracted through lower portion and appears to come from S2. Thus S1 and S2 act as two virtual coherent sources formed from the original source. Light waves arising from S1and S2 interfere in the shaded region and interference fringes are formed which can be observed on the screen . Applications of Fresnel's Biprism Fesnel biprism can be used to determine the wavelength of a light source (monochromatic), thickness of a thin transparent sheet/ thin film, refractive index of medium etc. A. ...

Optics for Optometry

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