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Buxton & District U3A Digital Photography Beginners’ Group

19 November 2013

Lesson 6: Understanding Exposure

Buxton & District

Digital Photography Beginners

Programme 19 September Exploring your camera

1 October You’ve taken some pictures now what? (Viewing pictures; filing on your computer)

15 October Printing & Composing a better picture (part 1)

29 October Camera modes/scenes & Composing a better picture (part 2)

5 November Simple editing to improve your pictures

19 November Understanding exposure

3 December Controlling exposure/focal length/perspective/composition for a better picture & Taking Pictures of people

17 December Everything you want to know about digital photography but never dared ask.

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Last Time

• Using Windows Photo Gallery to edit photos – Fixing “Red eye” – Straightening – Cropping – Adjusting exposure – Retouching

• Using Picasa to edit photos • A quick look at what Photoshop can do

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Homework

1. Try editing a few of your own pictures in Windows Live Photo Gallery or in Picasa:

• Fix red-eye

• Straighten

• Crop

• Adjust exposure

• Adjust colour

2. Bring any questions along next time

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This Time

How to improve my pictures.

• Understanding Exposure

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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

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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

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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

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What can you do about Lighting?

Live

with it

Find additional source

of light

ISO

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“Film Speed”



How big is the hole



For how long is the



2” 1” 1/2”

1/250” 1/125” 1/60”

1/30” 1/16” 1/8”

1/4”

1/500”

ISO

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Shutter

The 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

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“Film Speed”



How big is the hole



For how long is the



2” 1” 1/2”

1/250” 1/125” 1/60”

1/30” 1/16” 1/8”

1/4”

1/500”

ISO

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Aperture Like 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

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Aperture settings

The 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

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Shutter speed settings You 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 sec 1 sec 1/2 sec 1/4 sec

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

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What is the correct exposure?

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

ISO

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Exercise 1- Automatic Exposure

1. 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

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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

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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

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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

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Exercise 3 – Shutter Speed

1. 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 speeds i. 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

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What about aperture?

Change shutter speed Change 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

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Exercise 4 – Aperture

1. 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/8 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

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Exercise 5 – Manual Exposure

1. 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 shots i. 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

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“Film Speed”



How big is the hole



For how long is the



2” 1” 1/2”

1/250” 1/125” 1/60”

1/30” 1/16” 1/8”

1/4”

1/500”

ISO

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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

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ISO Settings ISO

ISO-100

ISO-200 Is 2x more sensitive than

ISO-100 Needs ½ as much light

Needs 1 stop less

light


ISO-100 Needs ¼ as much light

Needs 2 stop less

light


ISO-100

Needs 1/8 as much

light

Needs 3 stop less

light


ISO-100

Needs 1/16 as much

light

Needs 4 stop less

light

How sensitive is the film (or digital detector).

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Exercise 6 – ISO

1. 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

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Common Camera Modes

Portrait To attempt to blur out the background,

camera will try to use the smallest available f-stop.

Landscape camera will attempt to 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.

Usually available on SLRs

Not available on all compacts

Camera sets shutter speed and aperture to get programmed effect.

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Summary (what have you got to tinker with)

Exposure

Brighter/Darker Depth of field Motion / Still

ISO

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Homework

Go through Exercises 1-6 again at home in your own time.

Make sure you feel comfortable with:

• Controlling exposure

• Freezing / blurring motion

• Controlling depth of field

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Next Time

How to improve my pictures.

• Drawing together exposure / focal length / perspective

• Taking pictures of people

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Course notes I will put this presentation on the Buxton and District U3A website at : http://u3asites.org.uk/code/u3asite.php?site=179&page=25298 Or 1. Go to www.buxtonu3a.org.uk 2. Select “Groups” 3. Select “Digital Photography: Beginners” 4. Select “materials from previous sessions” from the links on right hand

side of page

http://u3asites.org.uk/code/u3asite.php?site=179&page=25298

http://u3asites.org.uk/code/u3asite.php?site=179&page=25298

http://www.buxtonu3a.org.uk/

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