What is ISO?

In traditional (film) photography

ISO (or ASA) was the indication of how sensitive a film was to light. It was measured in numbers (you’ve probably seen them on films – 100, 200, 400, 800 etc). The lower the number the lower the sensitivity of the film and the finer the grain in the shots you’re taking.

In Digital Photography

ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds (for example an indoor sports event when you want to freeze the action in lower light) – however the cost is noisier shots. I’ll illustrate this below with two elargements of shots that I just took – the one on the left is taken at 100 ISO and the one of the right at 3200 ISO (click to enlarge to see the full effect).

(you can see larger sized images of both shots here for the 100 ISO and here for the 3200 ISO)

100 ISO is generally accepted as ‘normal’ and will give you lovely crisp shots (little noise/grain).

Most people tend to keep their digital cameras in ‘Auto Mode’ where the camera selects the appropriate ISO setting depending upon the conditions you’re shooting in (it will try to keep it as low as possible) but most cameras also give you the opportunity to select your own ISO also.

When you do override your camera and choose a specific ISO you’ll notice that it impacts the aperture and shutter speed needed for a well exposed shot. For example – if you bumped your ISO up from 100 to 400 you’ll notice that you can shoot at higher shutter speeds and/or smaller apertures.

When choosing the ISO setting I generally ask myself the following four questions:

1. Light – Is the subject well lit?
2. Grain – Do I want a grainy shot or one without noise?
3. Tripod – Am I using a tripod?
4. Moving Subject – Is my subject moving or stationary?

If there is plenty of light, I want little grain, I’m using a tripod and my subject is stationary I will generally use a pretty low ISO rating.

However if it’s dark, I purposely want grain, I don’t have a tripod and/or my subject is moving I might consider increasing the ISO as it will enable me to shoot with a faster shutter speed and still expose the shot well.

Of course the trade off of this increase in ISO will be noisier shots.

Situations where you might need to push ISO to higher settings include:

• Indoor Sports Events – where your subject is moving fast yet you may have limited light available.
• Concerts – also low in light and often ‘no-flash’ zones
• Art Galleries, Churches etc- many galleries have rules against using a flash and of course being indoors are not well lit.
• Birthday Parties – blowing out the candles in a dark room can give you a nice moody shot which would be ruined by a bright flash. Increasing the ISO can help capture the scene.

ISO is an important aspect of digital photography to have an understanding of if you want to gain more control of your digital camera. Experiment with different settings and how they impact your images today.

Original Article(Click Here)

Learning About Exposure

The three elements are:

1. ISO – The measure of a digital camera sensor’s sensitivity to light
2. Aperture – The size of the opening in the lens when a picture is taken
3. Shutter Speed – The amount of time that the shutter is open

It is at the intersection of these three elements that an image’s exposure is worked out.

Most importantly – a change in one of the elements will impact the others. This means that you can never really isolate just one of the elements alone but always need to have the others in the back of your mind.

Three Metaphors for understanding the digital photography exposure triangle:

Many people describe the relationship between ISO, Aperture and Shutter Speed using different metaphors to help us get our heads around it.(Don’t know what ISO, Aperture or Shutter Speed means? More will be explained about them in the other articles.)

Let me share three. A quick word of warning first though – like most metaphors – these are far from perfect and are just for illustrative purposes:

The Window

Imagine your camera is like a window with shutters that open and close.

Aperture is the size of the window. If it’s bigger more light gets through and the room is brighter.

Shutter Speed is the amount of time that the shutters of the window are open. The longer you leave them open the more that comes in.

Now imagine that you’re inside the room and are wearing sunglasses (hopefully this isn’t too much of a stretch). Your eyes become desensitized to the light that comes in (it’s like a low ISO).

There are a number of ways of increasing the amount of light in the room (or at least how much it seems that there is. You could increase the time that the shutters are open (decrease shutter speed), you could increase the size of the window (increase aperture) or you could take off your sunglasses (make the ISO larger).

Ok – it’s not the perfect illustration – but you get the idea.

Sunbaking

Another way that a friend recently shared with me is to think about digital camera exposure as being like getting a sun tan.

Now getting a suntan is something I always wanted growing up – but unfortunately being very fair skinned it was something that I never really achieved. All I did was get burnt when I went out into the sun. In a sense your skin type is like an ISO rating. Some people are more sensitive to the sun than others.

Shutter speed in this metaphor is like the length of time you spend out in the sun. The longer you spend in the sun the increased chances of you getting a tan (of course spending too long in the sun can mean being over exposed).

Aperture is like sunscreen which you apply to your skin. Sunscreen blocks the sun at different rates depending upon its strength. Apply a high strength sunscreen and you decrease the amount of sunlight that gets through – and as a result even a person with highly sensitive skin can spend more time in the sun (i.e. decrease the Aperture and you can slow down shutter speed and/or decrease ISO).

As I’ve said – neither metaphor is perfect but both illustrate the interconnectedness of shutter speed, aperture and ISO on your digital camera.

Update: A third metaphor that I’ve heard used is the Garden Hose (the width of the hose is aperture, the length that the hose is left on is shutter speed and the pressure of the water (the speed it gets through) is ISO.

Bringing It All Together (Recap)

Mastering the art of exposure is something that takes a lot of practice. In many ways it’s a juggling act and even the most experienced photographers experiment and tweak their settings as they go. Keep in mind that changing each element not only impacts the exposure of the image but each one also has an impact upon other aspects of it (i.e. changing aperture changes depth of field, changing ISO changes the graininess of a shot and changing shutter speed impacts how motion is captured). The great thing about digital cameras is that they are the ideal testing bed for learning about exposure. You can take as many shots as you like at no cost and they not only allow you to shoot in Auto mode and Manual mode – but also generally have semi-automatic modes like aperture priority and shutter priority modes which allow you to make decisions about one or two elements of the triangle and let the camera handle the other elements.

A lot more can be said about each of the three elements in the exposure triangle. Check out other relevant posts on the topic at:

1. ISO
2. Aperture
3. Shutter Speed

Original Article(Click Here)