Chapter V Field stop and aperture stop视场光阑与孔径光阑5.1 Field stop and aperture stop 视场光阑与孔径光阑5.2 Filed of view 视场5.3 Vignetting and field lens 渐晕与场镜5.4 Telecentric system 远心系统5.5 Depth of focus and depth of field 焦深与景深5.6 Stray light in lenses 透镜中的杂散光5.1 Field stop and aperture stop一、Field stop and aperture stopAperture stop: The stop close to lens limits the size of the bundles of rays of axis point. It determines the amount of light reaching any given point in the image, therefore controls the brightness of image (image plane).Field stop:Just front of the focal plane limits the angle at which the incident bundles can get through to this plane (image plane). It determines the extent of the object or the field. (Field stop is usually made to coincide with image.)二、Entrance pupil and exit pupil: The image of aperture stop formed by preceding it.EP: The image of aperture stop formed by following it. The image of this stop, as formed by the lens is found to lie at the position .PL*Since is inside the focal plane, its image lies in the object space and is virtual and erect, PLPLPL called entrance pupil.* lies in the image space, called exit pupil.* , , are pairs of conjugated points. Any ray in the object space directed through one of Ethese points will after refraction pass through its conjugate point in the image space.三、Chief ray Any ray in the object space that passes through the center of entrance pupil is called chief ray. After refracting also pass through the center of the exit pupil.*Chief ray is a central ray of oblique rays.preliminary design of an optical instrument, must determine which one actually does the limiting?nlThe entrance pupil of the centric system is the image of the aperture stop formed by all lenses preceding it.The exit pupil is the image formed by all lenses following it.四、Stop between two lensesChief ray pass through the entrance pupil, the stop and the exit pupil.How to determine aperture stop?五、 Two lenses with no stop The periphery of any lens in system is a potential stop.Object at infinity, : entrance pupil. 1MNObject at A, : entrance pupil2PLDetermination of the aperture stopThe system consists of tow lenses and a stop.is the virtual image of the first ( )and a stop formed by ( )12P1lensL2lensL: Virtual image of the stop P formed by .0 2: Virtual image of the stop formed by .ls: Virtual image of the second lens formed by .21P1enFor all axial object points lying to the left of X, limits the entrance bundle of rays to the smallest 0Pangle.constitutes the entrance pupil.0constitutes the exit pupil.PFor all axial object point lying to the right of Z, is the entrance pupil and is the exit pupil.21P2PNominal aperture stop: The aperture stop of any system may change with a change in the object position.General rule: the aperture stop of the system is determined by that stop or image of stop which subtends the smallest angle as seen from the object point.Telescope and microscope (low power): usually aperture stop is selected at the large-sized objective lens.5.2 Field of view一、Field of view2W: object field and image fieldLook out at landscape through a window. Fig 1: The field of view is limited by the size of window and by the position of the eye. Window is field stop.General speaking, field stop is at image plane. ( such as telescope, microscope) The margin of reticle or film is field stop or frame.二、Field of a plane mirrorThe field of view offered by a plane mirror is very similar to that of a simple window. : observers eye, which constitutes the exit pupil. MN: The entrance pupil, virtual image of the eye pupil formed by mirror.Chief rays define the field of view.The object B and entrance pupil MN are in the object space. 三、How can you define the field of view of a convex mirror? 四、Field of a positive lensThe pupil of eye is an exit pupil and aperture stop.: the image of eye is an entrance pupil.MNThe field stop in this case is the lens itself.Object is in a position inside the primary focal point . Through each of three points 、 、 ABFPE, rays are drawn from to lens.LRefracted rays are directed through 、 、 , virtual image is located at .PELB*When converging lens is used as a magnifier, the eye should be placed close to the lens, since this widens the image-fieldangle.For visual visional optical instruments, the eye should be placed the exit pupil of optical system, such as telescopes and microscopes.五、Entrance window and exit windowEntrance window is the image of field stoop formed by all lenses preceding it.Exit window is the image of field stoop formed by all lenses following it.Both entrance and exit window are at infinity.六、Aperture angle and field angleAperture angle: Aperture angle in the object space. On-axis point subtend to the margin of entrance pupil.u: Aperture angle in the image space. On-axis image point subtend to the margin of exit pupil.Field angle: The center of entrance pupil subtended to the margi