Basics of Photography – Duration, Amount, and Sensitivity to Light (The Holy Trinity!)

When we talk about photography, what we are interested in primarily is light. Everything we see usually is due to a reflection of light on the object. Without going into too much physics, it is suffice to say that light is made up of particles called photons. These photons come out of a source (ie: the sun, a light bulb, etc.) and hit an object. The object can either absorb or reflect the photons which go into our eyes. Let’s illustrate this with an example. When we look at a green apple, what do we really see? Does the apple give off green light? The answer, which may surprise some people, is “no”. Our eyes actually are seeing a reflection of green light from the apple. When white light (which has all colours in it) strikes the apple, the pigments in the apple absorb every other colour and reflect green. This is actually pretty cool if you stop to think about it. Even more, black colour that we see is actually a pigment that absorbs all colours! Therefore it is very important to understand the nature of light in order to take photos effectively.

The fundamentals of photography (we won’t get into photographic terminology yet) revolve around three aspects of light: the “duration” of light, the “amount” of light, and the “sensitivity” to light by the viewer. All three of these things work synergistically with a simple increase or decrease relationship.The “duration” of light describes how long (time) the light has been beaming towards us. The sun which shines for much of the day, gives off a lot light if you think about it cumulatively. A short flash from a camera, gives off relatively little light. It is a little bit like filling buckets of water from a hose. Letting the hose run for a long time means a lot of water is in the bucket; whereas, a quick splash from the house yields little water. I know it seems redundant, but we really must bash these ideas into our head to be able to make effective photographic judgement when it comes to capturing once in a lifetime moments.

The “amount” of light is how much light is we see. Think about closing and opening the blinds of your window. You open the blinds; it allows a lot of light in. This is pretty simple. Another example of this is in our own eyes. During dark situations, our eyes actually open up more which allows more light to enter. This helps us adapt to darkness.

The last aspect is “sensitivity” to light. It helps to use our eye example again to help us explain this. Along with our eyes opening larger in dark situations, the retina (photon detectors) in the back of our eyes actually change chemically. They become more sensitive to light during darkness. Thus even a little bit of light can be perceived as a large amount of light. Thus by increasing or decreasing sensitivity of light, we indirectly change how much light we see.

I hope the previous descriptions were clear because now we are going to put them together. All three aspects can compensate for each other in interesting combinations. For example, having a large amount of light in a short time burst is pretty much the same as having a small amount of light which is has been left on for hours. The three interplay with one increasing while other decreasing and vice versa.If this is not completely clear let’s use the example of sunbathing. Let us say how long you sit in the sun for is the “duration” of light. The “amount” of light is how much clothing you wear to protect you from the sun. Lastly, how “sensitive” you are to light could be how much sunscreen you apply. Would it be suffice to say that all three play a role in whether you get sun burned or not? Could you compensate for each of them to get the same affect? A person who sits in the sun for a long time but who wears lots of clothes would get relatively the same sunburn as a person who sits in the sun for a little time but wears no clothes. By applying sunscreen, you decrease your sensitivity to light which is the same as putting on more clothes.

Now that you are an mini-expert in this, we can apply the theme of “duration”, “amount”, and “sensitivity” to photography terminology. The duration of light entering the camera is often called “Shutter Speed”. The amount of light is called “Aperture”. The sensitivity of the camera is called “ISO”. These terms may seem confusing for now, but rest assured with more use you will be comfortable using them. The three can be thought up as a holy trinity of photography.

Eventually by altering shutter speed, aperture, and ISO, the operator of the camera has full creative control over our photos. I know this is a lot of information to take in right now but it gets better from here. In following weeks post, we will focus (no pun intended) one by one on each aspect we discussed today and see their effects on photography in general (If you have been itching to apply some of the ideas we talked about, you will have your chance soon!).

FYI: Many times, automatic modes, such as NIGHT mode, are the cameras best guess to what settings to use. However, you should be able to come up with some ideas of what to do for night photography from the previous descriptions (Think how we get more light?).

Take home message:

Duration of Light = Shutter Speed

Amount of Light = Aperture

Sensitivity of Light = ISO