Talk to Midlothian Camera Club - February 10, 2009

Thank you.

Tonight: (A) 'Exposure'

(B) 'The History of Photography'

First ...

Exposure Summary of the Talk Please keep scrolling down to see large images and some text.
1	Under-exposure and Over-exposure © © © © © © ©
2	History © © © © ©
3	ISO - Time - Aperture © ©
4	ISO
5	Time © © © © © ©
6	Aperture © © © © © © © © ©
7	Can you trust the Camera? © © © © © ©
8	How to set the Camera
9	A few Photos © © © © © © © © © © ©
10	Depth of Field explanation © © © ©

Please ask questions - now or later

Under-exposure and Over-exposure

Photo 1

This photo has been exposed correctly.

Photo 1

Levels chart for the correctly exposed photo

Photo 2

This photo is too light. It has been over-exposed

Photo 2

Levels chart for the over-exposed photo

Photo 3

This photo is too dark. It has been under-exposed

Photo 3

Levels chart for the under-exposed photo

Photo 4

This photo is light. But is correctly exposed

Correcting Over- / Under-exposure

It is often possible to correct over-exposure/ under-exposure in Photoshop, but better to get it right in the camera.
Shooting in RAW gives more scope for correcting than JPG
Colour slides - must be exposed correctly
High contrast scenes - correction is not so easy
Try to get it right first time - less work, better results

History

The theory remains the same.

Equipment and materials continue to change.

Now, more latitude in materials and more automation.

Mid-1850s

Exposures were for several minutes.

Photography of moving subjects was not possible.

Head-stands were used in studios to keep subjects still.

Not many photos of people smiling!

Cartes de Visite

Not possible to photograph moving subjects.

Photography and printing in winter difficult - too dull.

1890s

New films allowed exposures of a fraction of a second.

Hand-held cameras became popular.

More amateurs took up photography.

Eastman Co - Regular Kodet camera - 1890s

Lizars' Advert - 1910

Mid-1900s

Long exposures still needed for colour film.
Cameras began to have built in exposure meters.

Now

Fully automatic cameras - exposure is less of a problem.

Digital Cameras - more scope for experimenting.

Digital Cameras - more scope for correcting.

ISO - Time - Aperture

Film Packet

Look Inside

Examples

SUNNY DAY: Perhaps 1/250 sec, f8, 100 ISO

DULL WEATHER: What to change?

ASSUME: '3 stops duller

i.e. only 1/8 of light

WHAT CHANGE is needed?

EITHER

1. longer time e.g. 1/30 sec - camera shake?

2. wider aperture e.g. f2.8 - depth of field?

3. higher ISO e.g. 800 ISO - grain / noise?

4. some combination of the above changes.

INDOORS:

long exposure? - Perhaps 1/2 sec, f4, 400 ISO

Use tripod or other support

Use Flash? Try it 'off camera'

Time

How Long?

Sport may need short shutter speed to capture the action. e.g. 1/1000 sec

Shutter speed for moving people and vehicles depends on:

- the speed of the movement.

- the distance from the camera.

- whether the subject is moving towards the camera or across the frame.

- the effect you want to create. e.g. Do you really want to freeze the action?

Fisheye Lens 1/3 sec f3.5

'Mind the Gap'

Camera held still for 1/8 second f6.7

Camera panned for 1/6 second f22

Camera panned for 1/125 sec f5.6 70-210mm lens @210mm

Camera still 1/250 sec f4 70-210mm lens @210mm

Waterfalls, fountains, and other moving water:

- Short shutter speeds capture all the droplets and spray, sharply. e.g. 1/1000 sec
This can look good when the scene is back-lit

- Long shutter speeds turn the water 'milky' e.g. 1/30 to several seconds
Moving water contrasts with surroundings.
Whether you like the result or not is personal preference.

Waterfall in Iceland

Aperture

Depth of Field

A small aperture, like f16, keeps most or all of a photo in focus.

Here are two views of Glen Ogle with the fence posts and the viaduct both in focus.

Winter

Autumn

A large large aperture, like f2.8, has a shallower depth of field, so keeps only the chosen area in focus.

Here are three views on the road to Glencoe, with more selective focus.

f2.8 - focus on the windscreen

© Copyright: Peter Stubbs -   please contact peter.stubbs@edinphoto.org.uk

f2.8 - focus on the piper

© Copyright: Peter Stubbs -   please contact peter.stubbs@edinphoto.org.uk

f2.8 - focus on the flowers

© Copyright: Peter Stubbs -   please contact peter.stubbs@edinphoto.org.uk

Relationship between Aperture and Shutter Speed

SMALLER 'f' number (e.g. f2)

= LARGER aperture

= MORE LIGHT

so needs SHORTER exposure

All these give the same result:

Examples: f2 1/1000 sec

f2.8 1/500 sec

f4 1/250 sec

f5.6 1/125 sec

f8 1/60 sec

f11 1/30 sec

f16 1/15 sec

f22 1/8 sec

Why is the in-between value f5.6, not f6?

- f8 is a measure of the diameter of the hole in the lens that lets in the light.

- f4 is double the diameter of f8, so lets in 4x as much light as f8.

- f5.6 is 1.414 ( = root 2 ) x the diameter of f8, so lets in 2x as much light as f8.

Explanation: f2 2 x 2 = 4

f2.8 2.8 x 2.8 = 8

f4 4 x 4 = 16

f5.6 5.65 x 5.65 = 32

f8 8 x 8 = 64

f11 11.3 x 11.3 = 128

f16 16 x 16 = 256

f22 22.6 x 22.6 = 512

The intermediate values above have been rounded. e.g. 16 x 1.414 = 22.624, but this is described as f22.

What is f2 and f4?

- f4 The focal length of the lens is 2 x the aperture. See red text on photo below.

- f4 The focal length of the lens is 4 x the aperture. See blue text on photo below.

Standard lens: 50mm = 2"

- Standard 2" lens with 1" aperture = f2

- Standard 2" lens with 1/2" aperture = f4

The photo below shows how the size of the hole changes when the aperture is changed.

Here, the diameter of the aperture has reduced to about 1/3 inch ( or 1/6 of focal length, so = f6)

Telephoto lens: 500mm = 20"

- Telephoto 20" lens with 10" aperture = f2. Much too bulky / heavy / expensive

- Telephoto 20" lens with 5" aperture = f4. Still bulky / heavy / expensive

My Pinhole Camera

designed to hold 16 in x 12 in sheets of photographic paper, not film.

Zoom-in to look at the Pinhole

Can you Trust the Camera?

Often, YES ... BUT not always.

1. The camera assumes that a picture tone is mid-grey

- Mid-grey is often a reasonable assumption - BUT

LIGHT SUBJECTS

- A snow scene or wedding dress at mid-grey looks wrong

- Try 1 or 2 stops more exposure to make it look LIGHTER

- 1 stop more = twice as much exposure. e.g at f8: 1/500 sec instead of 1/1000 sec.

Photo 1: What the camera saw: 1/500*, f5.6

Photo 2: What the camera saw + 1 stop: 1/250, f5.6

Photo 3: What the camera saw + 2 stops: 1/125, f5.6

Levels for Photos 1, 2, 3

1/500*, f5.6

1/250, f5.6

1/125, f5.6

* This is the reading I expected from the camera. But, on looking at the data for the photo, I see that it selected 1/750, f5.6. Perhaps I was pointing the camera down a little too far when I took the meter reading.

DARK SUBJECTS

- Dark subjects can also confuse the camera

A photo in a coal cellar, or a shop front painted black, should not be grey.

- Try 1 or 2 stops less exposure to make it look DARKER.

2. Can the camera cope with the range of brightness?

- Squint at a scene to see the possible outcome.

- Expose for the highlights. Don't lose detail in lightest parts.

- Consider a graduated neutral density filter for the sky

- On bright days, use 'fill in flash' outdoors

- For portraits, consider using a reflector

- If in doubt, bracket e.g at f8: 1/1000, 1/500, 1/250 sec.

- Then use the best

- combine more than one (possibly with HDR software)

3. Look at the levels chart on the back of the camera

- Try exposure compensation and see how the chart changes.

NOTE: Despite all the comments above, I find that it can be a good idea to ALSO take a photo at the exposure recommended by the camera. This may, in fact, turn out to be the best exposure, and with digital cameras there's no additional cost involved in taking an extra exposure.

How to Set the Camera

Full Auto

Av - Aperture priority

Tv - Shutter Priority

Manual

Full Auto

- Usually reliable.

- If the occasion is important and may difficult to 'go back and do it again e.g. a wedding, it may be a good idea to take a range of photos in 'full auto' mode, no matter what other photos are being taken.

Aperture Priority

- Useful to keep control over the depth of field.
e.g. to keep everything in focus in a landscape (or not).

- Maybe keep foreground and background in focus on a landscape.
e.g. use f.16 or f22.

- Maybe isolate one person in a crowd, as for some press photos.
e.g. use f.2.8 or f4.

- Check on the shutter speed required. Be prepared to use a tripod.

- Historic rule was don't hand-hold for > 1/focal length
e.g. Any speed longer than 1/50 sec with a 50mm lens needs a tripod

- Now with image stabiliser lens it is possible to hand-hold for longer
perhaps between 2x and 4x as long.

- Despite the above rule, it is surprising how much a tripod can help.

Shutter Priority

- Useful where you want to use a particular time and depth of field is less critical.

- for waterfalls or flowing water

- for fast action in sport

- for panning subjects

Manual

- This can prevent the camera from doing what it wants to do, if you think it's going to get things wrong. e.g.

- For copying photos, find the exposure using a 'grey card' then keep to that exposure for all photos, providing the lighting conditions do not change.

This should give a true copy of the photos, rather than one where the lighter and darker pictures have been adjusted by the camera.

- For panoramas, choose a day with no wide variations of light across the panorama. Find the exposure needed for an average part or important part of the scene. Set the camera to manual on that exposure for all settings.

- For scenes that are fairly monochrome in a dark of light colour, e.g. snow or dark or light building, use a grey card, lit and angled in the same way as the subject, then use manual - OR for digital photography (with no extra film or processing to pay for) it may be easier to just bracket the photo and select the best later.

A Few Photos

(a)

Direct and Reflected Light

(i) Flash lights the subject DIRECTLY

- A brighter flash is needed if the subject is further away

- Move 2x as far away: the flash has to be 4x as bright.

- Move 3x as far away: the flash has to be 9x as bright.

- Automatic flash can cope with this (within limits)

- Automatic flash at an outdoor event at night is only likely to illuminate the head of the person in front, not the performers on stage in the distance. (bad)

- Fill in flash, used for an outdoor portrait in bright light at daytime will fill in the dark shadows in the face, but will leave the background unchanged. (good)

1.5 seconds f4.5

Beltane Festival - Movement from the camera and the dancers