# Similar Triangles & Photography

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## Presentation Transcript

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Teacher’s Notes: Digital Image SourcesDigital images from space can be found at the following NASA web site: http://eol.jsc.nasa.gov/sseop/clickmap/ Click the map for images of that area. You can include in your search results information such as Altitude and Focal Length of the camera used by selecting FCLT and ALT at the bottom of the page. Images can be used freely if attributed to NASA. For added impact Google Earth (http://earth.google.com/) can be used to zoom from space to Tower Bridge, the Channel, etc. Depending on your location you may find better resolution images of your town on Microsoft’s Live Local site: http://local.live.com/ Information on aerial photography: http://landmap.ac.uk/ipc/ccrs/chapter2/chapter2_7_e.html

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StarterHow many, mm in 20 cm? cm in 3.75 m? m in 2.5 km? cm in 6 km? mm in 8 km?

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Similar Triangles & Photography

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Enlargement Factor =x =Reminderx cm8 cm10 cm25 cmFind the value of x.

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ExerciseIn each case, the pair of triangles are similar. Equal angles are marked. Find: i the relevant scale factor (enlargement or reduction) ii the missing length. ba

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How a Lens WorksLensDistance to objectFocal LengthObject HeightImage Height

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Example

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Enlargement Factor =x = 4000 mmx =

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Satellite PhotographyImage: NASA

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LensHeight above ground (Altitude)Focal length of cameraObject sizeImage sizeSimilar Triangles in Space

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Lens135 km90 mmx20 mmExampleEF =x = 30 000 000 mmx =

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Invergordon Academy Playing Fields Aerial Photo Altitude = 400 m Focal length = 152 mm

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Tower Bridge London Aerial Photo Altitude = 2500 ft (762 m) Focal length = 152 mmCalculate the span of the bridge.

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English Channel Photo taken onboard Space Shuttle Altitude = 126 miles (203 km) Focal length = 90 mmCalculate the shortest distance across the Channel. (marked)Image: NASA

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Actual DistancesTower Bridge – 244 m English Channel – 20 miles or 32 km

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Last Updated: 8th March 2018