# Cameras and Digital Imaging

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Cameras and Digital Imaging. (Some of this you can actually use in everyday life). An Important Number. The wider a camera lens opening (aperture), the more light enters. The greater the distance from lens to sensor (focal length), the more light is spread out and the fainter the image - PowerPoint PPT Presentation

### Text of Cameras and Digital Imaging

• Cameras and Digital Imaging(Some of this you can actually use in everyday life)

• An Important NumberThe wider a camera lens opening (aperture), the more light enters.The greater the distance from lens to sensor (focal length), the more light is spread out and the fainter the imageIf (focal length)/(aperture) is constant, the image is always the same brightness regardless of the size of the camera(focal length)/(aperture) = f-ratio

• F-ratio

Small f-ratioLarge f-ratioImage BrightnessBrightDimExposure TimeShortLongerDepth of FieldShallowDeepDiffractionLeastMost

• Depth of Field

• Depth of Field: f/2.7

• Depth of Field: f/8.0

• DiffractionAny time light encounters an edge (lens, mirror, opening of any kind), diffraction occursDiffraction limits the resolution of optical instrumentsRelatively unimportant for film but much more important for digital imagingFilm is a continuous recording mediumDigital imaging involves discrete pixels

• Diffraction

• Wide Aperture Lessens Diffraction

• Short Focal Length Lessens Diffraction

• Diffraction Creates Interference

• All Images Are Blurry

• The Airy Disk

• Why Bright Stars Look Bigger

• Image ResolutionTwo objects will not appear distinct unless their Airy disks are separateAiry disk size = 2.4 x wavelength x f-ratio500 nm and f/4 = 5280 nm = 5.3 micronsAbout the size of retinal cellsDidnt matter much for filmDoes it pay to have pixels smaller than the Airy disk?

• Bayer RGB Filter

• What is a Pixel?Digital cameras use Bayer RGB filter for color rendition of receptors are red sensitive, are blue sensitive and are green sensitiveMatches color sensitivity of eyeFour receptors (1R 2G 1B) = a pixel

• Super-Mega-PixelsPixels smaller than the Airy disk ( a few microns) contribute no resolutionDownside of mega-pixel camerasFewer photons per pixel = more noiseBloated file sizesProbably no harmBiggest problem with tiny cameras is inferior lenses

• More on MegapixelsHDTV = 2 megapixelsJames Cameron filmed Avatar with 2.2 megapixel camerasAnything over 5 megapixels probably unnecessaryMore pixels dont help, but dont hurt either

• Satellite ImagingOld Old SchoolShoot on filmDevelop on boardScan with oscilloscope and photocellReconstruct on groundExamplesLuna III 1959Lunar Orbiter

• Luna 3, October,. 1959

• Lunar Orbiter, 1966

• Lunar Orbiter, 1967

• Direct Film Imaging

• First Weather Satellite Image(Television Imaging)

• Spacecraft ImagingPhotomultiplier tubes are extremely sensitive and reliableTelevision-like technology used on spacecraft well into 1980sGalileo (launched 1989) was the first mission to use solid state imaging800 x 800 pixels

• Landsat Sensors

• Sensor Sweep

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