sp12 focus expose
Post on 05-Apr-2018
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Focus
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Lenses
Modern Compound Lens is made up of different kinds of glass ground to
different thicknesses and curvatures.
Good quality lens - better ground glass
Basic Parts:
Focus Ring
Aperture Control Ring
Depth of filed Preview Scale
Distance marker
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As the focal length increases,so does the magnification ofthe scene but the angle of
view narrows
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David Leventhal, Modern Romance
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3 factors that
affect d.o.f.
Aperture
Focal Length
Distance tosubject
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Digital depth of fieldWhy does f/8 give me one depth of field in
my film camera and another when I use
my digital camera?Depth of Field
Depth of field (DOF) is a term which refers to the areas ofthe photograph both in front and behind the mainfocus point which remain "sharp" (in focus).
Depth of field is affected by the aperture, subject distance,
focal length, and film or sensor format.
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same aperture different image sensor size
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Same lens focal length different sensor/film size
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Two major differences between lenses:
Lens Speed - the widest aperture to which the lens diaphragm can be opened, i.e. 2.0
Faster lenses open up to a wider aperture and admit more light; they can be used in
dimmer light or at faster shutter speed.
Focal Length - The focal length of a lens is defined as the distance in mm from the
optical center of the lens to the focal point, which is located on the sensor or film if the
subject (at infinity) is "in focus".
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Normal lens
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Wide
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Telephoto lens
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Fisheye
Macro
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Lightsensi*vematerial=imagesensor
+ memorycard
Createsavirtualratherthanphysicaloriginal
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Imagesensors:
Recordandstoretheimagetobephotographed(withthehelpofthememory
card,ofcourse.)
AtoDconversion-AnalogtoDigitalconversion
Readtheluminanceorbrightnessofthescene
CCD-ChargeCoupledDevice
ThedatecapturedbyaCCDsensorisreadonerowata*me-conveyorbelt
style.
CMOS-complementarymetaloxidesemiconductor
ThepixelsonaCMOSsensorincludeaddi*onalcircuitryforeachpixelthat
convertsthevoltageintoactualdigitaldata.Thedatacanbetransmiedtothe
camerainparallel=fasterdatatransfer.
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LIGHT METER READING!!Built in Camera Meter: reflective -measures the amount of lightreflected from a subject!into the camera!!Its very important to find out howyour camera reads light with itsbuilt in light meter:!Meters read - luminence -!All meters try to read a scene andthen average a middle grey
(18%).!Use an 18% grey card to help youmeter.!!
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Built-in meters:!Averaging meter - reads most of the image area andcomputes an exposure that is the !averaging of all the tones in the scene.!!Center-weighted meter - favors the light level at the center ofthe image, !often the most important part of the meter.!!Averaging and center weighted - averages a scene butgives more emphasis to the !center area of the the viewfinder
!!Multi-segmented meter - divides the scene into areas thatare metered individually and !then evaluated against a series of set patterns stored in thecameras memory. Tries to compensate for brightness of thesky.!!(Spot meter - reads only a small part of an image and is
useful for exact measurements of !individual areas.)!
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MeteringModes:
Matrix:Averagesceneswhereyouwantallareasoftheimagetobeintotheexposure.
Center-weighted:Any*methecameramightbefooled:backlitscenes,mainsubjectoffcenter,darksubjectsagainstlightbackgrounds,lightsubjectsagainstdarkbackgrounds,orlightonlightordarkondark.
Spot:Portraits,backlitscenes,mainsubjectoffcenter
Inmanycamerasthemeterreadingisinfluencedbytheauto-focuszone
usedtofocustheimage.
Howdoyouexposesothatalloftheimagecanbeexposedwell?
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Strategies to either override or adjust your cameras meter
1. Meter a gray target and use the light meter reading to calculate the best
exposure
fill the viewfinder with a gray card or other 18% gray object
press the shutter button halfway down to activate the light meter andhold it at that position to lock the exposure settings
frame the scene the way you want it and press the shutter button the
rest of the way to take the shot
2. Exposure lock:
or AE lock
The AE lock is usually a button that allows you to lock the exposure
setting for as long as you hold it down.
*make sure your target point (18% gray) is both in the same light and the
same distance from the camera as your subject to be photographed.
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Evalua*ng exposure
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Evalua*ngexposure
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Itdependsonwhereyoumeter
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HISTOGRAMSHistogram shows the brightness values of all of the pixels in an image.The height of each bar represents the number of pixels of a given brightness in the
whole photo.
Dark pixels Shadows Black: 0Middle-value pixels Midtones Middle Gray: 128Light pixels Highlights White: 255
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underexposed wellexposed over-exposed
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Unicorn Peak, Thunderclouds
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Shutter speed
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Shutter speed controls time
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Shutter Speed!!Shutter works with the aperture to
determine the amount of light enteringthe camera!!
!!!B 2 1 2 4 8 15 30 60 125 250 500 1000!
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What can you do with a long shutter speed setting?
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Aperture
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Aperture!! !Aperture refers to the size of the lens opening!! !Works like our pupil: wide open lets in more light!! !Size of the aperture is called an f-stop; the term stop! !refers to a change in exposure and is the the ratio between the diameter of
the aperture in the lens and the focal length of the lens. !!On a 50mm lens, f/2 is saying that the diameter of the aperture is 25mm. !
The ratio is this 50/25 = 2.!!f1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32!
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What is F Stop Anyway?
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WhatisF-Stop,Anyway?
F-stopisthefocallengthdividedbythediameterofthelens.
Forexample,a200mmf/4lenswillbe50mmwide.
200mm/50mm=f/4.
Thatiswhyf-stopistypicallywrienasF/4,meaning"focal-lengthover4"or"focal-lengthdividedbyfour".
Wheredothosenumberscomefrom?
Lensesaremarkedwithaseriesoff-stops,eachoneletsinhalfasmuchlightasthepreviousone.
Thelight-gatheringabilityofalensisdeterminedbyitsarea,andf-stopsaredeterminedbydiameter.
Areaisrelatedtodiametersquared.
Theprogressionoff-stops,1-1.4-2-2.8-4-5.6-8-11-16-22-32,arepowersofthesquarerootof
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Depth of Field:The distance between the nearest and farthest points that appear
in acceptably sharp focus in a photograph.
Small Aperture
More depth of field
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Large Aperture
Less Depth of Field
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Shutter speed and aperture!!Aperture controls:!a) how much light coming into the camera through the lens!b) depth of field (the range of area that the image is reasonably in focus)!!!Shutter speed controls!a) How long the light is coming into the camera!b) If an object in front of the camera is frozen or blurred!!
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