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Ghostly Images
TaskWhen a photo is taken with a flash, bright “disks” may appear as shown in the picture.Investigate and explain the phenomenon.
The GhostThe ghost is the image of a little flashed object, that was located out ofthefield depth.
Principle of the phenomenonThe light from a flash reflectsfrom a small surface in the unfocused area – it acts as a small source of light.Focused objectObject out of field depthPhotosensitivelayerlens
CameraCan always be approximated to a single convex lens with one aperture.Photosensitive layerA system of lensesPhotosensitive layerConvex lensAperture5
FocusObject located further than focused objectsFocused objectObject located closer than focused objectphotosensitive layerfocus depthlensiris
ApertureSmallaperture, big focusdepthBig aperture, smallfocusdepth
Focusingtheobjects
Lensmaker’s equationL0– focused object distanceL0’ – distance of the object’s      projection – distance of the ph. layerL1– distance of the ghost-generating objectL1’– distance of it’s projection
F-stop number (aperture)f – focus distanced – the size of the aperture
d – diameter of the apertures – diameter of the ghostly imageL0´ – distance between the ghostly image and the aperture = fL1´ – distance of the particle’s projectionSize of the ghostfor infinite focused object distance
Size of the ghostThe 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:
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. layerwpx –width of the image in pixelsActual size of the ghostly image in pixels – DpxExperimentsUsed in our experiments to determine the size of a ghostly image.
Experimental setupIndependent variablesApertureDistance from the lighted object to the lensDependent variablesSize of a ghostSmall particleFocusedobject
Method of measurementf1.8f19
Varying distanceConstant parametersFocal length f = 50 mmAperture numberA = 1,8 (d = 27,8 mm)Focused object distance L0 = 6 mParticle size p: negligibleVaried parameter–L1(the distance of the particles from the lens)
Varying distance [m]5,5                 5     4,5                 4                   3,5       3	        2,5	                2              1,5   1
Varying distanceProjected ghostly image size [mm]Particle distance [mm]
Constant parametersL1 = 1500 mmf = 50 mmL0 = 6 mp = negligibleVaried parameterA(by altering the diameter of the aperture)Varying aperture size
Varying aperture sizef1.8f2.8f3.3f5.6f8f13f19f22
Varying aperture sizeProjected ghostly image [mm]F-stop number (Aperture)
Constant parametersL1 = 1500 mmf = 50 mmL0 = 6 mp = 6mmVaried parameterA(by altering the diameter of the aperture)Varying aperture size
f1.8f2.8f3.3f5.6f8f13f19f22Varying aperture size
  The shape is dependent on the location in the image
on the distortions induced by the lens
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 reflectionOther observed effects
Given by aperture shape
Increasing theF-stop number increases the visibility of thiseffectShapeoftheghost
Shape dependenceFlaws of the lensThe optical enlargement isn’t the same in all parts of the lensColored edges
 Colored borders between light and shadow – caused by chromatic aberration Dependency of the refraction index of light on it’s wavelengthColored edges
Texture of the ghostly imageSmall particles (with their size comparable with the wavelength of light) (1<λ<100) have an easily  observable textureThis texture consists of concentric circlesDiffraction occurs on the small particlesOther, larger particles do not create ghostlyimages with these circles
ConclusionGhostly images are created when a particle outside the depth of field is litThe diameter of the ghostly image is mainly dependent on the particle distance and aperture sizeThe experiments confirm our theory with remarkable precisionOther effects can be observed in the ghostly image and we have described and explained their influenceThank you for your attention
Ghostly Images
Objective Nikon f1,8/50mm
 Double Gauss LensEquipmentChipNikon D80 RGB CCD
Dimension 23.6 x 15.8 mmLarge enough drops of water produce visibly separated multiple reflections of the flash and also refract light from other sourcesNon-typical reflection
Ghostly Images
TaskTaskWhen a photo is taken with a flash, bright “disks” may appear as shown in the picture.Investigate and explain the phenomenon.

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Ghostly Images

  • 2. TaskWhen a photo is taken with a flash, bright “disks” may appear as shown in the picture.Investigate and explain the phenomenon.
  • 3. The GhostThe ghost is the image of a little flashed object, that was located out ofthefield depth.
  • 4. Principle of the phenomenonThe light from a flash reflectsfrom a small surface in the unfocused area – it acts as a small source of light.Focused objectObject out of field depthPhotosensitivelayerlens
  • 5. CameraCan always be approximated to a single convex lens with one aperture.Photosensitive layerA system of lensesPhotosensitive layerConvex lensAperture5
  • 6. FocusObject located further than focused objectsFocused objectObject located closer than focused objectphotosensitive layerfocus depthlensiris
  • 7. ApertureSmallaperture, big focusdepthBig aperture, smallfocusdepth
  • 9. Lensmaker’s equationL0– focused object distanceL0’ – distance of the object’s projection – distance of the ph. layerL1– distance of the ghost-generating objectL1’– distance of it’s projection
  • 10. F-stop number (aperture)f – focus distanced – the size of the aperture
  • 11. d – diameter of the apertures – diameter of the ghostly imageL0´ – distance between the ghostly image and the aperture = fL1´ – distance of the particle’s projectionSize of the ghostfor infinite focused object distance
  • 12. Size of the ghostThe 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. layerwpx –width of the image in pixelsActual size of the ghostly image in pixels – DpxExperimentsUsed in our experiments to determine the size of a ghostly image.
  • 14. Experimental setupIndependent variablesApertureDistance from the lighted object to the lensDependent variablesSize of a ghostSmall particleFocusedobject
  • 16. Varying distanceConstant parametersFocal length f = 50 mmAperture numberA = 1,8 (d = 27,8 mm)Focused object distance L0 = 6 mParticle size p: negligibleVaried parameter–L1(the distance of the particles from the lens)
  • 17. Varying distance [m]5,5 5 4,5 4 3,5 3 2,5 2 1,5 1
  • 18. Varying distanceProjected ghostly image size [mm]Particle distance [mm]
  • 19. Constant parametersL1 = 1500 mmf = 50 mmL0 = 6 mp = negligibleVaried parameterA(by altering the diameter of the aperture)Varying aperture size
  • 21. Varying aperture sizeProjected ghostly image [mm]F-stop number (Aperture)
  • 22. Constant parametersL1 = 1500 mmf = 50 mmL0 = 6 mp = 6mmVaried parameterA(by altering the diameter of the aperture)Varying aperture size
  • 24. The shape is dependent on the location in the image
  • 25. on the distortions induced by the lens
  • 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 reflectionOther observed effects
  • 28. Increasing theF-stop number increases the visibility of thiseffectShapeoftheghost
  • 29. Shape dependenceFlaws of the lensThe optical enlargement isn’t the same in all parts of the lensColored edges
  • 30. Colored borders between light and shadow – caused by chromatic aberration Dependency of the refraction index of light on it’s wavelengthColored edges
  • 31. Texture of the ghostly imageSmall particles (with their size comparable with the wavelength of light) (1<λ<100) have an easily observable textureThis texture consists of concentric circlesDiffraction occurs on the small particlesOther, larger particles do not create ghostlyimages with these circles
  • 32. ConclusionGhostly images are created when a particle outside the depth of field is litThe diameter of the ghostly image is mainly dependent on the particle distance and aperture sizeThe experiments confirm our theory with remarkable precisionOther effects can be observed in the ghostly image and we have described and explained their influenceThank you for your attention
  • 35. Double Gauss LensEquipmentChipNikon D80 RGB CCD
  • 36. Dimension 23.6 x 15.8 mmLarge enough drops of water produce visibly separated multiple reflections of the flash and also refract light from other sourcesNon-typical reflection
  • 38. TaskTaskWhen a photo is taken with a flash, bright “disks” may appear as shown in the picture.Investigate and explain the phenomenon.
  • 40. Different particles with different size were used
  • 41. A lot of interesting effects were explained
  • 42. Type of photosensitive layer (film or pixels) has no influence
  • 43. Opponent did not accept my approach through geometric optics to a taskOverview
  • 44. ConclusionGhostly images are created when a particle outside the depth of field is litThe diameter of the ghostly image is mainly dependent on the particle distance and aperture size, which were investigatedThe experiments confirm our theory with remarkable precisionOther effects can be observed in the ghostly image and we have described and explained their influenceThank you for your attention

Editor's Notes

  1. Appendix - vysvetlenie