I think one of the most important things to understand in photography would be exposure. It controls everything about your images from the way it makes you feel to how sharp the image will turn out. Usually depending on how much light is available for the photograph but there are also other factors that control the exposure of an image. These factors make it able for us to achieve images with the same exposer but with different camera setting. You may be sacrificing things like detail for noise or shallow depth for a faster shutter. Learning how to control your exposure can help you become more creative with your photography. Even if your just taking a photo of someone riding a bicycle, with a slower shutter speed pan in the direction that the bicycle is moving to achieve a motion blur, your subject will be sharp and in focus while the background is blurred. Achieving the same exposure is possible with a faster shutter speed to freeze all the motion in the image by chaging to a faster shutter speed and compensating your ISO & Aperture
Factors that affect Exposure
1.Aperture
2.Shutter Speed
3.ISO
Aperture (f-stop)
Refers to the opening in the lens that lets light through to the cameras sensor. It opens and closes similar to the iris of your eye. The lower the number, the wider the opening and therefor more light can reach the sensor.
Example:
The Average 50mm Lens Ranges From f:1.8 to f:22
(Largest) f:1.8, f:2.8, f:4, f:5.6, f:8, f:11, f:16, f:22(Smallest)
f:1.8 is the largest lens opening & smallest f:#
f:22 is the smallest lens opening & largest f:#
As you close down the f:stop (make it smaller), the amount of light entering the camera reduced by ½. Example - f:1.8 to f:2.8
As you open up the f:stop (make it larger), the amount of light entering the lens is increased by 2 times. Example - f:22 to f:16
Shutter Speed
Refers to the length of time the cameras sensor is exposed to light. The job of the shutter is to freeze or blur motion, as well as opening and closing to allow light in to expose the sensor. The longer the exposure the more light there is to expose the image.
The shutter speed on a camera can range from a 30 second exposure to 1/8000th of a second exposure time. Most cameras today come with a "B" or bulb mode. This Setting allows you to keep the shutter open for as long as you want. Bulb mode is great to use when photographing things like Lightning and Fireworks or just being creative.
Usual numbers on a shutter speed dial:
2, 4, 8, 15, 30, 60, 125, 250, 500, 1000. (These numbers are read in fraction)
Example - 1/60th of a second
Shutter Speed Relationship to Light
Increasing the shutter speed from 1/60th to 1/125th doubles the shutter speed by
2(2x) and decreases the light by 1/2
Decreasing the shutter speed from 1/500th to 1/250th reduces shutter speed by ½
and increases the light by 2(2x)
ISO
Refers to the light sensitivity of the sensor. All cameras have an ISO sensitivity rating. As the number increase, so dose the sensitivity to light for Example: 100 ISO to 200 ISO. The speed doubles (2x), so dose the sensitivity to light. Now it’s like doubling the amount of light hitting the sensor. The higher the ISO the more sensitive the sensor is to light meaning that your image will also start appearing progressively grainer (digital noise) as your ISO gets higher.
Decreasing the ISO works in the opposite way. When the ISO Number is lowered so is its sensitivity to light.
Example: 400 ISO to 200 ISO.
The film speed is cut in half (½) and so is its sensitivity to light. Now it’s like reducing the amount of light hitting the sensor. An ISO's that is 1600 or under are usually safe to take photos with out having to worry about grain.
Light Meter
In camera light meters read reflective light (light that is reflected off of the subject) and help to make educated guess of the exposure. The sliding scale measures from -3 to +3 and each number represents 1 whole f-stop.
The light meter and sliding scale work hand in hand to give you the most accurate exposure reading. Line up the indicator as close to Zero for a correct exposure. Minus means your photograph may be under exposed and plus means your photography may be over exposed. Under or over exposing an image can be done for an artistic feel.
Light Meter Modes
Centre Weighted Metering - Average of centre plus surrounding
Evaluative Metering - Evaluates all points equally
Spot Metering – Reading of the center 3-6 degrees only
"Rule of Thumb"
Freeze Motion - Fast shutter speed (may need high ISO)
Show Motion - Slow shutter speed (may need low ISO)
Night or Long Exposure - Very slow Shutter Speed (tripod recommended)
Shooting in very dim light - High ISO
Shooting in very bright light -Low ISO
When to "Ignore" the Meter
Backlit Subjects: When there is more light behind your subject than there is illuminating it.
Backlight "fixes"
Remove the backlight
Change Positions
Fill light on the subject with a flash or reflector
Manually open aperture beyond what the light meter suggests.
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