Taking awesome photos: Part 2- Exposure

Welcome to part 2 of taking awesome photos!

Now that we have that pesky white balance sorted, lets look at understanding exposure. This embraces 3 different things:

• ISO
• Aperture
• Shutter Speed

ISO

Back in the days of film, which seem like forever away since the introduction of digital photography, the term ISO referred to film speed. ISO comes from the International Organization for Standardization which sets a world wide standard for measuring film speed. Hold on a sec you say, that acronym is wrong! Yes I thought that too, but found the answer here:

ISO’s name

Because “International Organization for Standardization” would have different acronyms in different languages (“IOS” in English, “OIN” in French for Organisation internationale de normalisation), its founders decided to give it also a short, all-purpose name. They chose “ISO”, derived from the Greek isos, meaning “equal”. Whatever the country, whatever the language, the short form of the organization’s name is always ISO.

Source: http://www.iso.org/iso/about/discover-iso_isos-name.htm

Anyway back to ISO setting in a digital camera. Back in the days of film the ISO referred to how light sensitive the film was. The faster the film, 400 and up, the less available light you needed. The slower the film, 200 and down, the more light you needed. This also determined how fast or slow your shutter could be and your aperture size. The downside to faster film was the amount of grain on the images. The faster the film, the more grain and less margin for error ie one stop under or over for 800 and 1600 ISO.

Now in digital photography, the ISO has a similar meaning but now refers to the sensitivity of the sensor inside the camera. The higher the ISO, the faster the shutter and less light you need, but the more digital noise you will have in your images.

All these number you scream – I still don’t get it! What does it all mean?  Basically it boils down to this: the higher the ISO setting the quicker the shutter speed. The lower the ISO, the longer you need to keep the shutter open for a properly exposed shot.

In everyday photography, you can leave the ISO on 100 or 200 and it won’t need to change. Don’t be fooled into thinking that you can leave the ISO at 800 as you will have a ton of digital noise in the images that you shoot. I personally leave my ISO on 100 or 50 as there is hardly any noise in the images.

Aperture

Aperture is measured in f-stops, for example f/2.8, f/4, f/5.6,f/8,f/22 etc. Each time you go down from one aperture to the next such as from f/4 to f/5.6, you cut the amount of light entering the lens by half. But then when you change the aperture from f/11 to f/8 the amount of light entering the lens doubles. Each half or double is referred to as a stop.

The aperture also controls the depth of field in a photo. The depth of field is the amount of your subject that will be in focus. A large depth of field, such as f/22 means that your foreground and background will be in focus. A shallow depth of field such as f4  is where the foreground is in focus and the background is blurry.

So the easiest way to remember is small f/stop number = small depth of field, large f/stop number = large depth of field.

Shutter Speed

Depending on the make and model of your camera, you may have shutter speeds as fast as 1/8000 to 30 seconds or a bulb mode where the shutter stays open as long as your finger is on the button. The shutter speed controls the amount of light coming through the lens. The same half and double principle that applies to aperture, is the same in regards to shutter speed.

The shutter speed is measured in fractions of a second and seconds  such as 1/125, 1/60, 1/30, 1/15 etc, then going down to 1 second and so forth. The bigger the denominator, the faster the shutter speed.

You will generally use a shutter speed of 1/60 or higher for handheld shooting. If you are using a slower shutter speed, you will need a tripod or a steady surface.

How to put them all together

As you can see in the above example, the difference of changing the shutter speed and tweaking the aperture.

The image on the left was shot with the following settings: ISO 80, f/stop of 25 and a shutter speed of 1/10

The image on the right was shot with the following settings: ISO 80, f/stop 4.5, and a shutter speed of 1/320

You can see the difference in the movement of the water in both pictures. The higher shutter speed “freezes” the water in the example on the right. On the left, the slower shutter speed makes the water appear “fluffy”.

Lets bring it all together, all the elements described above work together. If you change one, you need to adjust the others to compensate. For example if you close the aperture, then you need to adjust the shutter speed to a slower speed to allow more light through.  Or you can raise the ISO to compensate.

The following tables will help you in understanding exposure. They are some general settings that will help with your exposure settings on the fly.

Outdoor settings

Indoors, without flash

You can also check your exposure by pressing the shutter button half way to get a light reading and adjust the settings in order  to get the meter to read in the centre.

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