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Natural Science Forum / Physics / Optics / November 2004image of a point source
Hello, If we take the picture of a point source (obtained by passing monochromatic light through a 100um pinhole) with a camera (let's say with a 105mm lens with aperture f/2.8) focused on the pinhole, can the image of the source be the same as the diameter of the pinhole or does the diffraction (due to aperture in the lens) effect severely? can we use the formula 1.22*lambda*f/diameter to obtain the smearing effect of the diffraction? Also since the light is passed through pinhole and also a single slit diffraction occurs, can this effect also be seen in the image? I would appreciate your help about these questions. Burak > Hello, > [quoted text clipped - 10 lines] > I would appreciate your help about these questions. > Burak I am pretty sure that there are many profs at purdue who can answer your question. Asit stands, your question is very confusing. Bill >> Hello, >> [quoted text clipped - 7 lines] >> can we use the formula 1.22*lambda*f/diameter to obtain the smearing >> effect of the diffraction? It is clearer if you use the formula: Radius of first ring = 1.22*lambda/n.a. where na. is the cone semiangle at the final image, *provided* the pupil is filled uniformly, it doesn't matter how. In your example, n.a. = 1/(2*2.8). Focal length doesn't come into it. Brian can the image of > the source be the same as the diameter of the pinhole or does the > diffraction (due to aperture in the lens) effect severely? It would be the same (times magnification of your camera lens at your particular distance), if there were no aberrations of the lens or diffractin on its aperture. Do not confuse the latter with diffration on the pinhole. Diffraction on the pinhole sends "rays" of light at different angles, all of which would still be properly focused by the lens. A similar situation is in light projectors (LCD and DMD). There is diffraction on each pixel. However, since the pixels are in the focal plane of the lens, the projected image shows no effect of diffraction. Mike > Hello, > [quoted text clipped - 10 lines] > I would appreciate your help about these questions. > Burak |
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