Depth Of Field

Aperture is a key feature of DSLR cameras and one of the reasons they are so popular. They offer massive depth of field due to a large sensor size and lenses that have fast apertures.

Inside every DSLR lens there are aperture blades that control the amount of the light that can come through the lens and its then focused onto the sensor.

Here are some examples of the ways in which DOF can be used to enhance a photo:

To achieve shallow depth of field (blury subjects among sharp subjects) you need to be using an aperture of around f/4 and below. This is where the aperture blades are letting a lot of light in and will give you brighter images. When your aperture is around f/22 there will be a lot less light coming in and everything in your image will be in focus. Both a wide open and closed aperture have pros and cons.

Most lenses will be soft around there fastest aperture and you will often have to stop up to get sharp results. When your lens is at f/22 you need to compensate for the fallout of light by either slowing down your shutter speed or increasing your ISO. All three of these things are related and have a knock on effect when one is changed, but more on that later.

The below images were shot around between f/1.4 and f/4 as you can see some parts are in focus and some are not. This is what I was hoping to achieve by using such a fast aperture. Plus I was indoors so needed to let as much light as possible into the sensor so I could keep my shutter around 1/60 sec to avoid camera shake.

In this photo I was using a fast aperture so that the foreground was blurred to emphasise the leading lines of the wall and also draw your eye towards the human subject on the right of the image by blurring the left.
f/1.4
1/250
ISO 200
30mm

This was shot through a security door which had lines going through but because of the shallow depth of field and the fact I've focused on the background you can barely see the foreground. This is another use of aperture.
f/2.5
1/160
ISO 200
30mm

My Final Images

After experimenting with depth of field I have selected a few images which demonstrate the use of DOF and the different ways in which it can be used.

This shot demonstrates the use of foreground V background in DOF. This is a popular technique as you can be selective with what you want the user to focus on. For this particular photo you can tell there is a corridor in the distance but visually you can't see much about it so your imagination can wander.

The use of shallow DOF in this shot creates a nice blurred background and some nice bokeh from the lights. 

In this shot I used DOF to separate the 3 foreground subjects from the background as I wanted them to be the entire focus of the image. I think it helps create a sense of atmosphere and helps to add a sense of mystery to the location.

Shallow

This shot was about making only one element in focus. I chose something that was in the centre as I wanted a blurred foreground and background. This is often used to create a sense of visual hierarchy as you can choose what elements you want visible and what you want to be blurred out. The point of these shots was to select a point of focus that was around the centre of the image so that the foreground and background were both blurred.

Background V Foreground

This technique involves using a shallow DOF but focusing on an element in the background so that any foreground visuals are blurred. To achieve these shots I was shooting at around f2.8 on a sunny day this means I had to put my shutter speed up to around 1/800 and ISO 100

Foreground to background

This shot demonstrates my knowledge of aperture by being able to select an f stop that allows everything to be in focus. This is useful in many situations especially when used alongside leading lines as the audience can see everything in the photo. It also provides a sharper image as most lenses tend to be soft around large apertures but as they get smaller the image quality becomes sharper.

Aperture Range

The series of photos below were taken on a tripod and the exposure was kept the same. I was taking a shot each time I increased my aperture by a stop. The results is several images showing the graduation between small and large DOF. The first image was shot at f1.4 and as you can see there is only a very small part in focus. As the shots go on and the aperture increased up to f16 the background elements become more in focus. This is easier to demonstrate outdoors where there are several objects along the focal place that I can throw in or out of focus. This will be my next experiment.