How ISO, Shutter Speed and Aperture Affect Exposure and Metering

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I think that sometimes we tend to complicate things and make them more technical and difficult then they need to be. Understanding Iso, Shutter Speed and Aperture can be intimidating. When broken down individually learning what each does and how it affects the meter is your first step to controlling your camera in Manual Mode. Learn how to adjust these settings using your meter with the understanding of how they will affect the final image.

What Does it All Mean

ISO

International standard measurement of a cameras sensitivity to light
Exposure and sensor data readings are modified by amplifying the signal gain of the sensor
High Iso increases the amount of noise / grain in the photo
If the shutter speed and aperture settings cannot be changed Iso speed is another alternative to help center the meter to accomplish the correct exposure
Low light and night photography are example of when to adjust Iso

Shutter Speed

Refers to the amount of time light is exposed to the sensor
Values range from 30 to 1/8000^th of a second, depending on your camera
As you rotate the dial, values change in 1/3 steps, eg. 1.3, 1.6, 2, 2.5, 3, 4, 5, 6, 8, 10, 13, 15, 20, 25, 30, 40, 50, 60, 80,, 100, 125, 160, 200, 250, 320, 400, 500, 640, 800, 1000, 1250, 1600, 2000, 2500, 3200, 4000, 5000, 6400, 8000
The slower the setting the more chance of camera shake resulting a blurry picture
For faster moving objects use a faster shutter speed

Aperture

A measurement that controls the size of the opening in the lens, adjusted to control the amount of light entering the sensor
The size of this opening is measured in f-stops
It also determines the amount of area in focus in front and behind the main subject
Smaller numbers (larger fstop) eg. 2.8 allows more light in, produce crisp and clear images but only the main subject is in focus
A bigger number (smaller fstop) eg f22 means a smaller hole / less light, more of the scene is in focus but not as sharp and crisp, an excellent setting for creating sun flares

Pre Check List

Determine how you want your photo to look, eg. foreground and background in focus or isolated subject focus
Is your subject stationary or moving
How is the lighting, is it bright or dark
Are you using a tripod or not

For Sharp and Crisp Photos Stay in the Optimal Settings Zone

Iso set to 200 or lower
Shutter Speed of 1/30^th and faster, depending on how steady you are (if a little unsteady use a tripod)
Aperture f5.6 to f8, depending on the lens you are using
When outside of these settings, photo quality can degrade

4 Examples of Common Lighting Conditions / Settings for Landscape Photography

Pre- Sunrise / Post Sunset, A Little Dark but Enough Light to See What’s Around You

Iso set to 400 - 800, limited noise / grain at these setting
Aperture set to f4.5 - f6.3, at f6.3 I am still going to have some depth of field
*Shutter Speed adjusted until the meter is centered, aprox. 1/30th – 1/125th

The Sun is Low in the Sky or a Cloudy Day

Iso set to 200 - 400
Aperture set to f6.3 - f8
*Shutter speed adjusted to center the meter, aprox. 1/30 – 1/125^th

Bright Sunshine

Iso 200 or lower
Aperture f8 and smaller (bigger number eg f16)
*Shutter Speed adjusted to center the meter, aprox. 1/125th and faster

Night Time / Starry Skies

Use a tripod for longer exposures
Iso 400 and higher, keep in mind the bigger the number more noise / grain you will have
Aperture set to 2.8 or larger (smaller number), 2.8 works well for depth of field on my wide angle lens
Shutter Speed adjusted in seconds up to 30 or bulb mode for longer exposures over 30, a remote trigger is needed to use bulb mode
You will likely have to experiment with shutter speed to get an acceptable exposure

Adjustment Tips

Adjust all three settings, Iso, aperture and shutter speed to get the desired results / centered meter reading
Use of a tripod can help achieve optimal settings for sharpness / clarity
When capturing birds or other quick moving subjects use the fastest shutter speed as possible, you may have to adjust the Iso and aperture to keep a fast shutter speed
Exposure compensation is an alternative to help achieve good exposure by lightening / darkening the image
Pointing into bright light / sun the meter can be fooled, check the monitor after the shot to confirm proper exposure and adjust accordingly

*All Shutter Speed settings are dependent on the amount of available light; these settings may vary for your particular situation

Article and Photos by Mark McCulloch / www.photopaddler.com

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