Where, λ is wavelength & k is extinction coefficient.
Fig1: α observed at 300K for different semiconductors as function of vacuum wavelength of light.
2. Angular diameter: from a given point of view, it’s the angular measurement determining how large a sphere appears. Also called visual angle in visual sciences as shown.
Fig2. Angular diameter for distant objects.
To calculate use the given formula, Where: …show more content…
Biconvex lens
9. Camera Obscura: 19th century optical device commonly used by artists to make quick field sketches; which led to photography and modern camera. It a darkened box with one sided pinhole in a window blind.
10. Cassegrain telescope: It is a type of reflecting telescope. Its eye-lens is situated at the back of the primary mirror having orifice in the center. Light entering the telescope, reflects from primary to secondary mirror which again reflects it back through the primary mirror orifice to the eyepiece and we can see the image.
Fig.12 Cassegrain telescope>
11. Chromatic aberration: caused by a difference in light wavelength. The lens magnification varies with wavelength of each incident light ray. Thus, color fringing may occur at an image through a lens. Since a single lens cannot reduce chromatic aberration, two lenses of different optical properties are combined for correction. Fig.13 chromatic aberration>
12. Coma: is caused when there is a difference in distance of the incident light from the optical axis i.e. due to magnification difference. "Coma" refers to star tail toward the exterior like a comet and greatly impacts image quality in the field periphery. It is reduced by bending the lens or by using a lens combination symmetric about a central stop. Fig.14