# the focal length of spherical mirrors

Topics: Focal length, Wide-angle lens, Telephoto lens Pages: 3 (1513 words) Published: October 27, 2014

When a light incident on a polished surface it is reflected in such a way that the angle of reflection is equal to the angle of incidence. How will a ray through the centre of curvature of a concave mirror being reflected? Why? Define the radius of curvature and the focal length of a concave mirror. How are the focal length, the object distance and the image distance related? Which parameter of the mirror does the image distance approach as the object distance increases? How can a rough value of the focal length of a concave mirror be obtained? State reasons. What is the image distance equal to when the object distanto the point from which a collimated beam appears to be diverging after passing through the lens. The focal length of a thin lens can be determined by using it to form an image of a distant light source on a screen. The lens is moved until a sharp image is formed on the screen. The focal length f is then given by \frac{1}{f} =\frac{1}{u}+\frac{1}{v}\ ,

where u is the distance between the light source and the lens, and v is the distance between the lens and the screen. General optical systems

Thick lens diagram
For a thick lens (one which has a non-negligible thickness), or an imaging system consisting of several lenses and/or mirrors (e.g., a photographic lens or a telescope), the focal length is often called the effective focal length (EFL), to distinguish it from other commonly used parameters: Front focal length (FFL) or front focal distance (FFD) is the distance from the front focal point of the system to the vertex of the first optical surface.[1][2] Back focal length (BFL) or back focal distance (BFD) is the distance from the vertex of the last optical surface of the system to the rear focal point.[1][2] For an optical system in air, the effective focal length (f and f′) gives the distance from the front and rear principal planes (H and H′) to the corresponding focal points (F and F′). If the surrounding medium is not air, then...