PhotoSoc Mini Lecture – Exposure


So this is a summary of today’s lecture. Because of the room change and various technical challenges I never had time to show you the demos i wanted to which really help understand these settings.

I tried battling with the union site but it doesn’t like me, so im posting here for now and will transfer it later.


What is Exposure ?

Essentially exposure is the image we create whilst letting light fall onto the cameras sensor. It is controlled by 3 separate camera function each of which we discuss below.

The word “exposure” is quite literally referring to how we are “exposing” the sensor to the light.

It is a balance of these three functions…

Shutter Speed + Aperture + ISO

… which will allow you to achieve the creative effect you desire, whilst not letting in too much light (Overexpose) or too little (Underexpose).


Shutter Speed

You can imagine the shutter like a set of curtains on a window. It is usually closed, so no light is allowed in. We can quickly open these curtains for a set duration to let some light fall onto the sensor.

The longer the curtains are open, the more light is allowed to collect onto our sensor and the brighter the image gets.

shutter_speed

On my camera ?

All SLR cameras and now, many point and shoot cameras allow you to control shutter (now even some phones have this control!).

There are generally two modes in which you can set the shutter speed, these are “Manual Mode” and “Shutter Priority Mode”.

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Canon and Nikon “Shutter Priority” Mode symbol on Dials

Shutter Priority Mode will allow you to set a shutter speed, and the camera will automatically adjust aperture values (explained below) to keep the exposure correct.

Manual Mode gives you full control over both shutter speed and aperture. As will become clear, to get exposure correct, you must balance these two options.

Creative (side) Effects

  • longer shutter speed will allow for motion blur. This means anything moving in your scene will begin to become blurry. Use this to emphasize or create motion in your scene!
  • longer shutter speed also means that any movement in the camera whilst the shutter is open will be recorded leading to a blurry image.
Pace of City Life - Markela DLR Motion Blur

In this shot I used a slow shutter speed to allow the moving DLR train to blur out. A faster shutter speed would have frozen it, removing the effect I wanted to capture

blog_islou_co_uk-4848-2 - Copy

An even slower shutter speed of a few seconds can allow for a light painting effect for anything emitting light. This was shot on a photosoc trip to london a few years back!


Aperture

The aperture is a ring which can be opened or closed to allow or restrict light and its path into the camera.

wide aperture is denoted by a smaller number which lets in more light while a tight aperture is denoted by larger numbers and lets in less light.

Below are a series of images shot at various apertures. Now the light in the image hasn’t changed, but thats only because the camera was set to “aperture priority mode” and has automatically varied the shutter speed to compensate for the light lost with the aperture.

Also take note of the Depth of Field changes in the images below, this is further explained in the “Creative Effects” section below.

aperture

 

On my camera ?

All SLR cameras and now, many point and shoot cameras allow you to control aperture.

There are generally two modes in which you can set the aperture, these are “Manual Mode” and “Aperture Priority Mode”.

Picture4

Canon and Nikon “Aperture Priority” Mode symbol on Dials

Aperture Priority Mode (Used  in the example images above) will allow you to set an aperture value and the camera will automatically adjust shutter speed values to keep the exposure correct.

Manual Mode gives you full control over both shutter speed and aperture.

 

Creative (side) Effects

First lets understand the term “Depth of Field”. This is used to describe how much ahead and behind of your focus point is still acceptably sharp or “in focus”.

So if we say a “shallow depth of field” we mean that there is very little ahead or behind our focus point (or subject) which is in focus. This is usually seen in images as a nice blurry background which people usually associate with “professional” photos.

A Larger or Wider aperture will reduce your depth of field whilst a Smaller aperture will increase your depth of field bringing more into focus.

Here is an example of a shot taken in London of a friend with a Wide Aperture (f.1.8), take a look at the background and how small points of light become big soft circles. The wide aperture also allows me to draw in lots of light in this otherwise fairly dark scene.

LCH_6508-copy

A shot with a wide aperture of my friend Aron in london. The wide aperture leads to a nice out of focus background and gives me the ability to collect lots of light into my camera sensor.


ISO

Photographs used to be recorded onto film, which was essentially a chemically coated light sensitive strip. The sensitivity of this strip was determined by the film manufacturers and measured in units called ISO (or ASA) which was just an international standardisation. The entire roll of film would be  the same sensitivity so once loaded into the camera this couldn’t be changed.

With digital cameras this light sensitive film has been replaced with a light detecting block usually referred to as the “sensor”. Unlike the film days we can change the sensitivity of the block as we wish.

The Higher the ISO the More Light is captured, BUT this also leads to a More Noisy Image.

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Here is a shot from a christening. This was in a very dimly lit part of the church and the camera was pushed to ISO 1600. Below the image is a 100% zoomed crop.

In the example image above shot at ISO 1600 the noise becomes evident, in A you can see random colour squares appearing out of place. In B you can see how an otherwise smooth gradient looks blocky and dirty rather than clean. This is off a modern and high quality camera. Its unlikely an entry level camera will be this clean at ISO 1600.

It is therefore always advisable to keep ISO as low as you can, but make sure you don’t compromise on the other settings either! Never allow yourself to miss a shot because you did not want to push the ISO up. Also worth noting, if you do find yourself needing to use very high ISO, the grain it produces tends to look fantastic when images are converted to black and white!

Lecture Printout

Here is a download of the lecture printout in PDF format: 2011-10-27 – Exposure (Ben)-revised by louis 2012

I hope this helps expand on the lecture! Of course I’m always around in meetings, workshops and trips to help out and answer any questions 🙂


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