Optometrists and opthalmologists, instead of using the focal length to specify the strength of a...
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![Page 1: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/1.jpg)
Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the
power or diopter of a lens.
The power (diopter) = 1 / fFor example, a 20 cm focal length
lens has a power of 1 / 0.20 = 5.0 Diopters
![Page 2: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/2.jpg)
Cameras
![Page 3: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/3.jpg)
Camera Settings
Shutter speed: how long the shutter is open. Speeds faster than 1/100 s are normally used. Fast action requires a very small shutter speed.
![Page 4: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/4.jpg)
Camera Settings
F-stop: changes the diameter of the iris diaphragm to control the amount of light reaching the film.
The SMALLER the f-stop, the LARGER the opening.
![Page 5: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/5.jpg)
The f-stop determines “depth of field”.
A larger f-stop (a smaller opening)- will produce an image
where everything is in focus.
A smaller f-stop (a larger opening)- will produce an image in
which only the subject is in focus and everything in the foreground and background is out of focus.
![Page 6: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/6.jpg)
A TELEPHOTO lens has a longer focal length to magnify images.
A WIDE-ANGLE lens has a shorter focal length.
![Page 7: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/7.jpg)
TelescopesRefracting telescopes have two lenses,
the objective and the eyepiece.
The eyepiece lens has a smaller focal length.
The objective lens has a larger focal length.
![Page 8: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/8.jpg)
MicroscopesMicroscopes also have
two lenses, the eyepiece and the objective.
The eyepiece lens has the longer focal length.
The objective has the smaller focal length.
![Page 9: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/9.jpg)
Fresnel Lens
The weight and bulk of a large diameter lens can be reduced by constructing the lens from small wedged segments that follow the curvature of the original lens and collapse down to a thin layer.
![Page 10: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/10.jpg)
Augustin Fresnel Fresnel invented
this type of lens in 1822.
![Page 11: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/11.jpg)
Fresnel lenses can take a small diverging light source and change it into a powerful straight beam of light.
![Page 12: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/12.jpg)
Small plastic Fresnel lenses are sold at office supply stores as “Magnifying Lenses”
Fresnel Lenses are also used in overhead projectors
![Page 13: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/13.jpg)
Large glass lenses that have Fresnel surfaces surrounding a small light source have provided an invaluable contribution to coastline areas for more than 150 years. These lenses are used in…..
![Page 14: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/14.jpg)
Lighthouses
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Tests showed that while an open flame lost nearly 97% of its light, and a flame with reflectors behind it still lost 83% of its light, the fresnel lens was able to capture all but 17% of its light.
Because of its amazing efficiency, a fresnel lens could easily throw its light 20 or more miles to the horizon.
![Page 16: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/16.jpg)
![Page 17: Optometrists and opthalmologists, instead of using the focal length to specify the strength of a lens, use a measurement called the power or diopter of.](https://reader035.fdocuments.in/reader035/viewer/2022062317/5a4d1b687f8b9ab0599b1c9e/html5/thumbnails/17.jpg)