UGC NET Paper 1 Mathematical Reasoning & Aptitude.pdf
Ghostly Images
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2. Task When a photo is taken with a flash, bright “disks” may appear as shown in the picture. Investigate and explain the phenomenon.
3. The Ghost The ghost is the image of a little flashed object, that was located out ofthefield depth.
4. Principle of the phenomenon The light from a flash reflectsfrom a small surface in the unfocused area – it acts as a small source of light. Focused object Object out of field depth Photosensitive layer lens
5. Camera Can always be approximated to a single convex lens with one aperture. Photosensitive layer A system of lenses Photosensitive layer Convex lens Aperture 5
6. Focus Object located further than focused objects Focused object Object located closer than focused object photosensitive layer focus depth lens iris
9. Lensmaker’s equation L0– focused object distance L0’ – distance of the object’s projection – distance of the ph. layer L1– distance of the ghost-generating object L1’– distance of it’s projection
11. d – diameter of the aperture s – diameter of the ghostly image L0´ – distance between the ghostly image and the aperture = f L1´ – distance of the particle’s projection Size of the ghost for infinite focused object distance
12. Size of the ghost The particle is not a perfect point source of light, it has a certain diameter p (we have to count it in). There is an increase in the size of the ghostly image described by our final formula:
13. We wanted to measure the exact size of the ghostly image on the chip, thus we introduced a size coefficient. One pixels size: wm –width of the ph. layer wpx –width of the image in pixels Actual size of the ghostly image in pixels – Dpx Experiments Used in our experiments to determine the size of a ghostly image.
14. Experimental setup Independent variables Aperture Distance from the lighted object to the lens Dependent variables Size of a ghost Small particle Focusedobject
19. Constant parameters L1 = 1500 mm f = 50 mm L0 = 6 m p = negligible Varied parameter A(by altering the diameter of the aperture) Varying aperture size
26. on the structure of the aperture Different color of the edges of the ghostly image The texture of the ghostly image Particles with non-typical light reflection Other observed effects
30. Colored borders between light and shadow – caused by chromatic aberration Dependency of the refraction index of light on it’s wavelength Colored edges
31. Texture of the ghostly image Small particles (with their size comparable with the wavelength of light) (1<λ<100) have an easily observable texture This texture consists of concentric circles Diffraction occurs on the small particles Other, larger particles do not create ghostlyimages with these circles
32. Conclusion Ghostly images are created when a particle outside the depth of field is lit The diameter of the ghostly image is mainly dependent on the particle distance and aperture size The experiments confirm our theory with remarkable precision Other effects can be observed in the ghostly image and we have described and explained their influence Thank you for your attention
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38. Task Task When a photo is taken with a flash, bright “disks” may appear as shown in the picture. Investigate and explain the phenomenon.
43. Opponent did not accept my approach through geometric optics to a taskOverview
44. Conclusion Ghostly images are created when a particle outside the depth of field is lit The diameter of the ghostly image is mainly dependent on the particle distance and aperture size, which were investigated The experiments confirm our theory with remarkable precision Other effects can be observed in the ghostly image and we have described and explained their influence Thank you for your attention