Glossary
Definition of a lens: The classic definition of a lens is that it is an optical system consisting of at least two refracting surfaces out of which one is curved and other can be any non linear surfaces like parabolic or electrical.
Normal lens: A lens which gives a normal view to the human eye.
Wide angle lens: Gives a wider view of the subject
Telephoto lens: Gives a closer view of the subject.
Chromatic aberration: It is a type of distortion in which there is a failure of a lens to focus all the colors of the spectrum at a same converging point. It occurs because lenses have a different refractive index for different wavelength of light. he refractive index decreases when they increase in wavelength.
Spherical Aberration: This is an optical problem that happens when all the incoming rays end up focusing at different parts after passing through the spherical surface and end up in different parts or a spots across lens axis. In other words the parallel rays of incoming light do not converge at the same point because of this spherical aberration can affect resolution and clarity. There by making it hard to get a sharp image.
Coma: Coma is an aberration in which light rays pass through off axis point causing the lens to focus at different point resulting in a blur. It is a lens aberration producing a symmetrical distortion of points in an image. In coma the image of a point source of a light is prevented from being broad into focus. It is a lens defect which results in points of light appearing in image not as points but as disk with comet like tails. This refers to the blurring of the object at the edge of field of view.
Astigmatism: This defect arises due to development of different curvatures along different planes of a lens. This lens aberration makes a single point lighting source impossible to focus as a true point. It is imaged instead either as of a two shot lines at right angles at different distances from the lens.
Flare: This is yet another defect which occurs because modern lens is made up of various elements, which within themselves, are also lenses. All these lenses reflect a certain amount of light back to the surface and some of it may go to the film there by causing a ghost image. Thus flare is caused by the partial reflection of light from the lens.
Image Magnification: It is the ratio of the size of an object with relation to the image. This ratio is a linear relation, let us say if the distance between the lens and the object is “u” and the distance between the lens and the image formed is” v” then we have the magnification that is “v/u”, if ‘v’ is longer and ‘u’ is smaller we will get a magnification of a higher size. On the other hand if the “u” is larger and “v” is shorter then we will get a image of a smaller size. This is applied in terms of photography that is to say when the subject and the lens distance is smaller that is” u” is smaller and “v” is larger we get a telephoto, we get a enlargement we get a bigger image on the other hand when the” u” is larger and “v” is shorter we get a wide angle image of the subject that is to say if the lens moves closer to the object the image becomes larger and vice versa.