Lens Flare and Diffraction

Lens flare is a result of light refracting off the surface of a lens, it shows up as artefacts on your images, often as blue, green or red circles, low contrast or hazy areas and it can be used to creative effect. It is harder to achieve with newer lenses which have anti-reflective coatings, but can be achieved when there is a bright light source at the edge of the lens.

Diffraction causes the Starburst effect, seen on bright points of light when the Aperture is small, the light diffracts off the narrow gaps between the aperture blades. Again it can be used to creative effect.

Exposure

Image of a photographer taking a photograph

Exposure:
The action of exposing the sensor or film in a camera to light.

A correct exposure has detail in the highlights and shadows. Correct exposure means an image with maximum detail, that gives us the most options in editing.

Too much light leads to overexposure:
images that are too bright and have no detail in the light or highlight areas.

Too little lights leads to underexposure:
images that are too dark and have no detail in the dark or shadow areas.

The amount of light entering the camera is controlled by the aperture, shutter speed and  ISO (Sensitivity).

Exposure Triangle

Every photograph is an exposure, created through the use of three controllable factors: Aperture, Shutter Speed and ISO. Changing one of these settings means changing the other settings. Each element has a trade off that effects the image.

Exposure is measured in ‘stops’ each stop is half or double the amount of light of the previous number. For example f/4.0 is half as much light as f/2.8, 1/125th second is twice as much light as 1/250th second, ISO 400 is four times as much light as ISO 100. – on a digital cameras this is broken down further into thirds of a stop, each click on the camera control dials changes the exposure by 1/3 of a stop.

Viewfinder and Exposure Meter

An image of a camera viewfinder

The exposure meter should always have the line in the center to start with, this should give you the correct exposure or close to it.

The camera meter has a variety of exposure modes including:
Spot meter – takes the exposure from a small area of the lens 10% or less
Centre Weighted – takes the reading from the centre of the lens
Matrix metering – automatic metering that takes readings from lots of areas of the viewfinder and averages them out.

Correct Exposure

image showing correct exposure

Correct Exposure

A correct exposure has detail in the highlights and shadows. Correct exposure means an image with maximum detail, that gives us the most options in editing.

In this image the highlight or lightest areas (the clouds) have lots of detail with no ‘blown out’ areas.

image of an overexposed photograph

Overexposure

Too much light leads to overexposure:
images that are too bright and have no detail in the light or highlight areas.

An image showing an underexposed photograph

Underexposure

Too little lights leads to underexposure:
images that are too dark and have no detail in the dark or shadow areas.

Histogram

Image showing a camera histogram

A graphical representation of the camera’s exposure reading, a guide to getting a correct exposure.

On Canon cameras
:
1. Press the play button to view an image
2. Press info until the histogram appears
On Nikon cameras:

1. Press the play button to view an image
2. Press up on the control buttons until histogram appears

Apertures

The aperture is the gap in the centre of the blades of a lens. It controls HOW MUCH light enters the camera. When the aperture is adjusted it decreases and increases the amount of light entering the camera, by making the whole larger or smaller (a large or small aperture).

The aperture is measured in stops indicated by a fraction:
f/1.4 f/2.0 f/2.8 f/4.0 f/5.6 f/8 f/11 f/18 f/22 each aperture is half or double the amount of light of the preceding aperture. The smaller the number the bigger the aperture f/1.8 is a very LARGE aperture and lets in lots of light f/22 is a SMALL aperture and only lets in a small amount of light.

Depth of Field

Depth of field diagram

Depth of Field refers to how much of a photograph is in focus. It is an effect specific to photography caused by the shape of lens elements. It is controlled using the aperture, the larger the aperture (smaller the number) the less of the image is in focus.

When we use a small aperture more of the image is in focus than when we use a large aperture. We refer to this as Shallow or Deep Depth of Field. A useful way to remember which is which is large number, large depth of field, small number, small depth of field.

Aperture – Shallow Depth of Field

An imgae of poppy heads showing shallow depth of filed

Apertures – Shallow Depth of Field
A small amount of the image is in focus.

Large Aperture (Small number) f/5.6, f/4, f/2.8 and lower

Small Number – Small Depth of Field

Shallow Depth of Field

Depth of field also becomes shallower as you get closer to a subject.
The choice of lens also affects depth of field.
Telephoto or Long focal length lenses create a shallower depth of field.
Wide angle lenses create a deeper depth of field.
When you are choosing how much depth of field you want in your image, you need to consider APERTURE, LENS CHOICE and DISTANCE FROM YOUR SUBJECT

Shallow Depth of Field

Image showing shallow depth of field, circles of confusion and bokeh

Shallow depth of field can also create an interesting affect, particularly with bright areas, such as raindrops, reflections on water and streetlights. These are called ‘circles of confusion‘. The shape or aesthetic quality of these circles is called Boke or Bokeh (pronounced Bow-ca), a phrase that has become popular in recent years on social media and online forums.

Shallow Depth of Field

Image of a cow showing shallow depth of field

Shallow depth of field works really well in portraits, it helps to concentrate the image on the most important area, the eyes.

Shallow Depth of Field

Shallow depth of field in a photograph of bluebells in a wood

A large aperture of f/2.8 has been used to create shallow depth of field, isolating this Bluebell from it surroundings.

Aperture – Deep Depth of Field

Image showing a Deep Depth of Field

Apertures – Deep Depth of Field
A large amount of the image is in focus

Small Aperture (Large number)  f/11, f/16, f/22 and higher

Large Number – Large Depth of Field

Deep Depth of Field

Image showing Deep Depth of Field

A deep or large depth of field is excellent for landscape images, or where you want a large amount of detail, with everything sharp. f/22 was used for this image so that the bridge was sharp from the front of the image to the back. Because it was dark, a very long exposure was required of 2 minutes.

Deep Depth of Field

Image showing Deep Depth of Field

A deep or large depth of field can be effective for portraits where the background is relevant to the main subject or environmental portraits.

Shutter Speeds

Image showing the effects of shutter speed

The shutter is a curtain in front of the sensor. It determines HOW LONG the camera sensor is exposed to light for. Shutter speeds are measured as seconds or fractions of a second as stops of light and are described as FAST or SLOW.  For example 1/125th or one hundred and twenty fifth of a second is a FAST shutter speed, 2″ or two seconds is a SLOW shutter speed.
1/125, 1/60,  1/30, 1/15, 1/8, 1/4, 1/2, 1”,  2”, 4″

Shutter Speed controls the length of time the sensor is exposed to light for. It also controls whether movement is frozen or blurred. A fast or high shutter speed freezes motion, a slow or long shutter speed causes motion blur.

Camera Shake

Camera shake is the unintentional blurring of an image, usually because the shutter speed is too low. In this image the blur was intentional to give the effect of a moving vehicle, however usually the image should be sharp. Camera shake can be prevented by using a shutter speed close to the focal length of the lens when handheld, for example with a 30mm lens a minimum of 1/30th second shutter speed should be used.

Controlling Movement with Shutter Speed

Controlling motion blur

A fast shutter speed 1/125, 1/250, 1/500 and above will freeze movement. How ‘frozen’ the movement will be, depends upon the speed of the subject moving and how fast the shutter speed is. Sometimes, you want a subject to have just a little movement, to show that it is actually moving. This guide can be used as a starting point and then gradually reducing the shutter speed will increase the amount of apparent movement.

Fast Shutter Speed

Fast Shutter Speed

In these images the shutter speed is fast enough to freeze motion. The shutter speed used to freeze this dancer in mid air was 1/250th Second.

Fast Shutter Speed

High Shutter Speed Example

A fast or high shutter speed of 1/800th Second was used to freeze the waves in this image. 

Fast Shutter Speed

Fast shutter speed image

A fast or high shutter speed was used to create this image, not only to freeze the motion of the subject and the background, but also to prevent camera shake caused by the vehicle the photograph was taken from.

Fast Shutter Speed

Fast Shutter Speed

In this image the shutter speed has been high enough to freeze motion, but also just slow enough to capture a small amount of movement at the end of the horses legs.

Slow Shutter Speed

Example of slow shutter speed

A slow shutter speed 1/15, 1/8, 1/4 second and below will cause movement to blur in the image. If the camera is handheld, this will cause camera shake. If the camera is on a tripod or stabilised in some other way, it can be used to creative effect. In this photograph the shutter speed was 15 seconds, this has caused a lot of blur in the image, which conveys the atmosphere of a busy market.

Slow Shutter Speed

Image showing light trails

In this photograph the camera was fixed on a tripod to the back seat of the car, a slow shutter speed was used, so that when the car was moving light trails were created.

Slow Shutter Speed

Image showing intentional camera movement

A slow shutter speed has been purposely used in this image to create intentional blur.

Slow Shutter Speed

Example of slow shutter speed

A slow shutter speed has been used to give an impression of a busy city. This image would perhaps not work so well if the traffic was static.

ISO

The ISO (International Standards Organisation) setting, controls the sensitivity of the camera’s sensor. It determines how much light is needed to capture an image. Increasing the ISO or sensitivity means that photographs can be taken in less light.
ISO like Apertures and Shutter Speeds is also measured in stops of light half or double the previous one.
The higher the number the more sensitive the sensor is for example 3200 high sensitivity.
100. 200. 400. 800. 1600. 3200. 6400

Example of ISO noise

ISO

Example of ISO and noise

The higher the ISO the more noise there will be in an image. In a sports situation like this, a high shutter speed may be needed to capture the action and there may not be enough light to use a low ISO.

Fortunately there are tools in Adobe Lightroom to reduce this noise.