Ray Optics (the action of a lens)

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Ray Optics (the action of a lens) is the fourth lecture within the Waves and Optics section of PH1011. It covers imaging, with pinholes and lenses.

Pinholes
Imaging can be achieved through pinholes - the light from an object will be focused through a narrow area, but will be upside down, dim and fuzzy due to interference of multiple light beams. Making the pinhole smaller will make the image duller, rather than sharper.

Lenses
Glass with correct surface angles can be used to refract the light so that all incident light from one point converges on the other side of the glass - this is how lenses work. The paraxial approximation allows this to work so long as angles of incidence and refraction are less than 10°; Snell's law runs the necessary calculation. This causes the image to be sharp, although still inverted.

Summary
Pinholes are not useful. Lenses focus incoming rays to a single point, allowing a sharp and bright image to form.