An Idiot’s Guide to Exposure

a.k.a. John’s Guide to Exposure

What is exposure?Exposure is “measuring and controlling the amount of light from a scene which is captured in a picture”.

Under exposed Over exposed

What affects Exposure

How sensitive is the film (or digital detector)

“Film Speed”

How much light is there on the subject “Lighting”

How big is the hole letting light into the

camera “Aperture”

For how long is the camera collecting light

“Shutter speed”4”2”1”

1/2”

1/250”1/125”1/60”

1/30”1/16”1/8”

1/4”

1/500”

ISO

Why should I care?Auto and “program” modes measure the lighting and automatically adjust exposure

Sometimes you can get a different effects with different settings.

Sometimes Auto is just wrong.

So many cameras give you extra modes to set the exposure differently

ISO

ISO

What can you do about Lighting?

Live with itSpend money on lights

ISO

ShutterThe shutter blocks all light from exposing the film UNTIL you press the button. Then it quickly opens and closes, giving the film a brief flash of light.

Closed Open Closed

The longer the shutter is open the more light reaches the film.

ISO

ApertureLike the Iris in the eye, the aperture opens and closes to let more or less light in

• Small aperture• Less light• Darker image

• Large aperture• More light• Brighter image

ISO

Aperture settingsThe size of the Aperture is measured in “f-numbers”, or “f-stops”.

1 stop difference lets in twice as much light (picture is twice as bright)

Examples:

moving from f/16 to f/8 is TWO STOPS brighter.

moving from f/5.6 to f/8 is ONE STOP darker

moving from f/4 to f/2.8 is ONE STOP brighter

f/2.8

f/4

f/5.6

f/8

f/11

f/16

f/22

Brighter

Darker

ISO

Shutter speed settingsYou can control the length of time the shutter remains open by setting the SHUTTER SPEED

Examples:½ sec exposure is ONE STOP darker than a 1 sec exposure.

1/125 exposure is TWO STOPS brighter than a 1/500 exposure.

A 1/1000 exposure is THREE STOPS darker than a 1/125 exposure.

2 sec1 sec1/2 sec1/4 sec

1/15 sec1/30 sec1/60 sec1/125 sec1/250 sec1/500 sec1/1000 sec1/2000 sec

Open for long time / slow shutter speed / more light / brighter

Open for short time / fast shutter speed / less light / darker

1/8 sec

ISO

What is the correct exposure?

Under exposed Over exposed1/125 f5.6 1/60 f5.6

ISO

Exercise 1- Automatic Exposure1. Set your camera to Auto mode.

2. Find where your camera tells you what shutter speed and aperture it is going to use when you are about to take a picture.

3. Take some pictures, taking particular notice of the shutter speed and aperture as you take each picture.

4. Take pictures in a variety of lighting conditions:i. Indoors and outdoors

ii. Scenes with bright and dark areas

iii. Sunny day & grey day (if you can find them!)

iv. Sun behind you / sun in front of you.

5. Are you happy with the exposure in all of the pictures?

ISO

What if Auto gets it wrong?Exposure compensation function

Typically adjusts exposure by ± 2 stops.

Exposure compensation (this shot will be 1 1/3 stops underexposed)

ISO

Exercise 2 - Exposure Compensation

1. Set your camera to program mode.

2. Find the exposure compensation adjustment on your camera (if you have one).

3. Try taking several pictures of the same scene at different exposures:

i. Shoot the same scene with set to +2; +1; 0; -1; -2

ii. Try this with several different scenes

iii. Find some scenes which have a both bright and dark areas

ISO

Shutter speed – so what?

1/60 sec 1/4000 sec

Fast (short) shutter speed freezes movement of the subject (or camera)

Slow (long) shutter speed blurs movement of the subject (or camera)

ISO

Exercise 3 – Shutter Speed1. Set your camera to Shutter Priority

2. Find out how to adjust the shutter speed in this mode.

3. Change the shutter speed:i. Find the shutter speed and aperture on the camera display.

ii. How does the camera tell you if it can’t set the aperture to get a correct exposure at your chosen shutter speed?

4. Take pictures of moving objects:i. Take some shots at fast shutter speed (1/250 or faster)

ii. Take some shots at slow shutter speed (1/30 or slower)

5. Find out what happens at slow shutter speedsi. Zoom in as far as your camera will allow (longest focal length or highest “x” zoom) and

shoot outdoors at shutter speeds of 1/30 or less.

ii. Zoom out as far as your camera will allow (shortest focal length or 1x zoom) and shoot a similar scene at shutter speed of 1/30 or less.

iii. Come indoors – how slow do you have to set the shutter speed to get a good exposure (without flash)?

iv. Stay indoors – what happens when you take pictures at speed of around 1/10 or 1/15.

ISO

What about aperture?

Change shutter speedChange aperture to keep exposure

1/3 f22 1/13 f11 1/50 f5.6

Motion in foreground frozen as shutter speed increases

Foreground in focus in all shots

Background focus more blurred as aperture increases

ISO

Exercise 4 – Aperture1. Set your camera to Aperture Priority

2. Find out how to adjust the aperture in this mode.

3. Change the aperture:i. Find the shutter speed and aperture on the camera display.

ii. How does the camera tell you if it can’t set the shutter speed to get a correct exposure at your chosen aperture?

4. Take pictures of scenes with object(s) in the foreground which are clearly separated from the background:

i. Take shot at a wide aperture (f/4 or larger)

ii. Take shot at small aperture (f/22 or smaller)

5. Take pictures in a range of lighting conditions.

6. Can you always find a viable shutter speed for the aperture you have chosen?

ISO

Exercise 5 – Manual Exposure1. Set your camera to Manual Exposure (if you have one)

2. Find out how to adjust the aperture and shutter speed in this mode.

3. Find out how your camera tells you if the shutter speed / aperture combination gives a “correct” exposure.

4. Try taking a range of shotsi. take pictures in various lighting conditions

ii. “freeze” motion

iii. show motion by “blurring” the image

iv. isolate an object from the background (object in focus, background blurred)

v. foreground and background both in focus

5. Do you have more of a range of shutter speed or aperture?

ISO

What about ISO?How sensitive is the film (or digital detector).

• Sometimes you have to use a very slow shutter speed even at maximum aperture (shaky picture).

• If you had a more sensitive film you could speed up the shutter & stop the shake.

• With a digital camera you can just change the setting.

• Digital cameras usually have automatic ISO setting.

• Digital cameras usually also allow manual ISO selection.

ISO

ISO settings

ISO-100

ISO-200Is 2x more sensitive than ISO-100

Needs ½ as much light

Needs 1 stop less light

ISO-400Is 4x more sensitive than ISO-100

Needs ¼ as much light

Needs 2 stop less light

ISO-800Is 8x more sensitive than ISO-100

Needs 1/8 as much light

Needs 3 stop less light

ISO-1600Is 16x more sensitive than ISO-100

Needs 1/16 as much light

Needs 4 stop less light

How sensitive is the film (or digital detector).

ISO

Exercise 6 – ISO1. Find out how to adjust the ISO on your camera.

2. Set ISO to Auto.

3. Take pictures in a range of lighting conditions – note the ISO, shutter speed and aperture.

4. Choose the shutter speed (shake/freeze/blur) and aperture (depth of field) then see if you can adjust the ISO to get a correct exposure.

5. Take a picture with the lowest ISO you have and a similar picture with the highest ISO. Can you see any difference in quality of the image?

ISO

Common Camera Modes

Movie/Video In movie mode, Digital cameras can capture live streaming video.

Macro/Close-Up this mode used for taking close-up pictures.

Party/Night longer exposures to capture darker scenes. Usually used with flash, and some nice motion effects can be created.

Portrait To attempt to blur out the background, camera will try to use the smallest available f-stop.

Landscape camera will attempt capture detail in foreground and background by using high f-stop.

Sports To freeze motion, camera will use the highest shutter speed possible .

Aperture Priority You set the f-stop and the camera tries to set shutter speed to get a good exposure .

Shutter Priority You set the shutter speed, and the camera tries to set the aperture to get a good exposure .

Manual Full manual control, you must set both the shutter speed and the aperture.

Stitch For creating multi-shot panoramas, this mode helps to combine several shots into one wide scene. Good fun .

Summary (what have you got to tinker with)

Exposure

Brighter/DarkerDepth of field Motion / Still

ISO