Exposure Basics

As a keen photographer you’ll want to escape that Auto setting on your camera as soon as possible. To do this you’ll need to understand exposure. That is basically, in the simplest terms, the amount of light you put on the sensor.

There are three factors to concern yourself with:

  • ISO Setting
  • Shutter Speed
  • Aperture

ISO Setting

This all about the available light you’ve got. Ideally you want that number to be kept on a low setting, say 100. If there’s not much light then up-ing the ISO will make the sensor more sensitive to light and allow you to take photos in lower light conditions. However high ISO settings will lower the quality of the shot.

If you are on your widest aperture setting and the shutter speed is too slow due to the low light then you can up this setting and that will speed things up a bit.

Shutter Speed

This is how long the shutter is open for. You can have very fast speeds like 8000th of a second or you can keep the shutter open for 30 seconds. If something is moving very quickly your 8000 setting with freeze it to a stop. Slower shutter speeds will blur anything that’s moving, which is great for being creative.

If you are holding your camera in your hand and you want your shot to be sharp use this rule. Use a shutter speed of at least the same number as the mm of the lens you are using. So if you are hand holding a zoom in at 300mm then you’ll need a shutter speed or at least 300mm.

The longer the shutter is open though the more light that can get in. If not enough gets in then your photo will be dark (under exposed). So for fast speeds like that you will need plenty of light or a higher ISO setting.

On the other end of that, if say you want to blur some motion, you’ll need a slow speed, but if there’s too much light then your photos will be washed out (over exposed). You can set the ISO to its lowest setting if you’ve closed your aperture as far as it will go.


This is the best setting of all. Basically  – high f numbers = less light allowed in, low f numbers = more light allowed in.

But there’s another very important factor to consider. High numbers gives you a larger depth of field and low f numbers give you less depth of field. Depth of field is how deep the focal point is. Say you focus on something 3 feet away. Your focal point will be set to 3 feet. But depending on the f setting will give you things also in focus both closer and further away from that 3 feet setting. Put it on a low f number and only the 3 feet mark will be in focus, move from that and it will be out of focus and start to blur. Whereas if you get a high f number then things 2 feet in front and 4 feet away will also be in focus. This technique is great for portraits where the face is pin sharp but the background is nicely blurred out.

The rule to remember is you must have the right amount of light hitting the sensor. So if you go with a high f number you will need a slower shutter speed to compensate. And vice versa of course.

Depth of field varies between lenses. Wide angle lenses will have deep depth of field but telephoto ones will generally be more shallow.

The ability to get lots of light in to a lens is the single biggest cost in photography. The faster the lens, or in other words, the lowest the f number can go, the more expensive the lens will be. It means it can operate in lower light settings or allow faster shutter speeds than its slower counterparts.

Are you made for this?...