Photography is all about light.  Three controls affect the amount of light reaching the camera’s sensor: aperture, shutter speed and sensitivity. Each one also has a creative impact on the image.

Aperture

Aperture is a fancy word describing the size of opening on the lens. Aperture is denoted in f-stops.

aperture size light effect creative effect uses
smaller aperture (larger f#)
smaller opening
less light reaches the sensor narrower depth of field – less of the photo in focus separate a subject from a distracting background, portrait, close-up (macro),
larger aperture (smaller f#)
wider opening
more light reaches the sensor wider depth of field – more of the photo in focus landscapes, crowds

Shutter Speed

A camera’s shutter is like a curtain that opens and closes in front of the sensor. It determines how long light reaches the sensor. Shutter speed is measured in seconds or fractions of seconds. At slower shutter speeds, use a tripod to prevent camera shake and the resulting blurry images.

shutter speed light effect creative effect uses
faster shutter speed less light reaches the sensor freezes motion clear shots of sports, kids, animals, objects in motion
slower shutter speed more light reaches the sensor blurs motion dreamy shots of moving water, low light shots, fireworks, night shots

Sensitivity

The sensor’s sensitivity to light is measured in ISO.

ISO light effect creative effect uses
lower sensor is less sensitive to light, sharper, more detailed image daylight outdoor shots
higher sensor is more sensitive to light less detail is captured resulting in more digital noise (grain)
in image
high speed sports, action, low light situations

And now for the fun bit.  Some smart folks have divided each of these three controls into “stops” as shown in the following table. Each stop up doubles the light. Each stop down halves the light. This allows the photographer to change the creative effects while maintaining equivalent exposures.

aperture (Av) shutter speed (Tv) sensitivity (ISO)
exposure f-stop depth of field seconds motion ISO image quality
brighter f 1 shallow 1 blurred 12800 more grain
f 1.4 1/2 6400
f 2 1/4 3200
f 2.8 1/8 1600
f 4 1/15 800
f 5.6 1/30 400
f 8 1/60 200
f 11 1/125 100
f 16 1/250 50 sharp
f 22 1/500
darker f 32 deep 1/1000 frozen

The following four images have equivalent exposures.

aperture (Av) shutter speed (Tv) sensitivity (ISO)
base image f 5.6 1/250 200
image 2 f 8 ½ light 1/125 2x light 200
image 3 f 4 2x light 1/250 100 ½ sensitivity
image 4 f 11 ¼ light 1/125 2x light 400 2x light

With the above tools and some knowledge of artistic composition, you are on your way to great photos. Now go and have some fun!

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