Tips & Tutorials

Lens Basics #4: Deep Focus

Deep focus, where all elements in an image are in focus, is a technique that is often used in landscape photography and street photography. Here, we learn about 4 factors that affect deep focus. How about trying them in your next photo shoot? (Reported by Tomoko Suzuki)

Lens Basics top image

 

4 factors for easy deep focusing

 

4 factors in deep focusing

“Deep focus” refers to a state where all elements in an image are in focus. You can call it a technique that is the opposite to creating bokeh. There are 4 factors in achieving deep focus: Focal length, aperture, depth and shooting distance. When you photograph, it is important not just to have a good understanding of the concept of “depth-of-field” (the area of an image that appears in focus), but also good control of these 4 factors.

The 4 factors are:
Focal length: Depth-of-field is greater at short focal lengths, and shallower at longer focal lengths.
Aperture: Depth-of-field is greater at smaller apertures, and shallower at larger apertures.
Depth: This refers to the distance between foreground, medium ground and background elements. The flatter the image (less distance between the elements), the easier it is to achieve deep focus. The more depth in an image, the harder it is to achieve deep focus. 
Shooting distance: The further the camera from the subject, the larger the depth-of-field. The nearer the camera to the subject, the shallower the depth-of-field.

In other words, the easiest way to ensure you achieve deep focus is to use a wide angle lens, set it at the smallest aperture, position your camera as far away from the subject as possible, and make sure that there is very little depth in your image.

Deep focus tip: Using a narrow aperture slows down your shutter speed, which makes images taken in dim or dark places more prone to camera shake. To counter that, use the ISO Auto mode.

Let’s take a closer look at each of the factors that affect deep focus.

 

Focal length

The examples below were shot at different focal lengths, but with the same f-number (f/11), and the shooting distance was adjusted so that the pillars appear to be the same size. At the shorter focal length (24mm), the depth-of-field is greater, with the elements in the background in focus. Meanwhile, at the longer focal length (70mm), the depth-of-field is narrower—note how even at f/11, the school building in the background is out of focus. This shows how using a wide angle lens, which gives you a very short focal length, can help achieve deep focus more easily.

Shorter focal length (24mm)

Shot with the EF24-70mm f/2.8L II USM at 24mm, f/11

EOS 5D Mark III/ EF24-70mm f/2.8L II USM/ FL: 24mm/ Aperture-priority AE (f/11, 1/160sec, EV-0.3)/ ISO 100/ WB: Manual

Longer focal length (70mm)

Shot with the EF24-70mm f/2.8L II USM at 70mm, f/11

EOS 5D Mark III/ EF24-70mm f/2.8L II USM/ FL: 70mm/ Aperture-priority AE (f/11, 1/100sec, EV-0.3)/ ISO 100/ WB: Manual

 

Aperture

The images below were shot from the same position, but with different apertures. The image shot with the smaller aperture (f/16) achieves deep focus—the image is sharp all the way to the background. However, the one shot with the larger aperture (f/1.4) has a background that is very highly defocused. For images like the ones below, where the distance between the camera and the subject is short but the image has a lot of depth, narrowing the aperture all the way to f/16 enables you to put the entire image sharply in focus.

Narrow aperture (f/16)

Shot with the EF50mm f/1.4 USM at 50mm, f/16

EOS 5D Mark III/ EF50mm f/1.4 USM/ FL: 50mm/ Aperture-priority AE (f/16, 1/80sec, EV+0.3)/ ISO 100/ WB: Manual

Large aperture (f/1.4)

Shot with the EF50mm f/1.4 USM at 50mm, f/1.4

EOS 5D Mark III/ EF50mm f/1.4 USM/ FL: 50mm/ Aperture-priority AE (f/1.4, 1/8000sec, EV+0.3)/ ISO 100/ WB: Manual

 

Depth

Depth in an image is not absolute. You can increase the depth in an image by adjusting the composition. I used the same wide aperture (f/1.4) for both images below, but shot the image on the left head-on to create a relatively flat image (no depth). It is completely in focus, which shows that you can also achieve deep focus with a large aperture, as long as the image is relatively flat and you are shooting from the direct front. In the image on the right, I used a diagonal composition to create some depth. Notice how the parts of the image nearest to and furthest away from the camera are out of focus.

For an example of deep focus and use of angles in travel photography, check out:
Irresistible Tips from Professionals in Travel Photography

No depth (head on)

Shot with the EF50mm f/1.4 USM at 50mm, f/1.4, from the front

EOS 5D Mark III/ EF50mm f/1.4 USM/ FL: 50mm/ Aperture-priority AE (f/1.4, 1/40sec)/ ISO 125/ WB: Manual

With depth (diagonal composition)

Shot with the EF50mm f/1.4 USM at 50mm, f/1.4,diagonal angle

EOS 5D Mark III/ EF50mm f/1.4 USM/ FL: 50mm/ Aperture-priority AE (f/1.4, 1/40sec)/ ISO 125/ WB: Manual

 

Shooting distance

The following images were both shot with the same aperture (f/5.6), but from different shooting distances. When the camera is further away from the subject (the 100cm example, left), the depth-of-field is larger. When it is nearer to the subject (the 70cm example, right), the depth-of-field is shallower. From this, we can conclude that when we are shooting a distant scene, we do not necessarily need to use an extremely narrow aperture to achieve deep focus. Somewhere between f/5.6 to f/8 should be sufficient to put the entire image in focus.

Further (100cm)

Shot with the EF24-70mm f/2.8L II USM at 27mm, f/5.6,shooting distance: 100cm

EOS 5D Mark III/ EF24-70mm f/2.8L II USM/ FL: 27mm/ Aperture-priority AE (f/5.6, 1/200sec, EV+0.3)/ ISO 100/ WB: Manual

Nearer (70cm)

Shot with the EF24-70mm f/2.8L II USM at 27mm, f/5.6, shooting distance: 70cm

EOS 5D Mark III/ EF24-70mm f/2.8L II USM/ FL: 27mm/ Aperture-priority AE (f/5.6, 1/250sec, EV+0.3)/ ISO 100/ WB: Manual

 

Important things to note when using deep focus technique

1. Understand that depth-of-field is about the image plane, not a point in focus

Shot with the EF50mm f/1.4 USM at 50mm, f/2

EOS 5D Mark III/ EF50mm f/1.4 USM/ FL: 50mm/ Aperture-priority AE (f/2, 1/250sec, EV+0.3)/ ISO 100/ WB: Manual

Diagram showing field of focus
 

In the example above, take note of how all the chess pieces that are arranged horizontally within the field of focus are in sharp focus, but the pieces arranged vertically are all out of focus. Why is this so? To put it simply, the camera considers all objects that are the same distance away from it to be on the same plane. As long as it is within the depth-of field, all images in that plane will be in focus, as the camera will not differentiate between different points in the same plane. Keep that in mind when you make your decision about aperture setting and how much you want the image to be in focus.

 

2. Using an f-number that is too large could cause image quality to deteriorate

Shot with the EF24-70mm f/2.8L II USM at 70mm

The area in the red frame when enlarged
EOS 5D Mark III/ EF24-70mm f/2.8L II USM/ FL: 70mm/ Aperture-priority AE (1/30sec, EV+1.0)/ ISO 100/ WB: Manual

Shot with the EF24-70mm f/2.8L II USM at 70mm, f/8, f/22
 

We learnt that using a narrower aperture (larger f-number) generally increases depth-of-field, which makes your image sharper. However, if you use an aperture that is too narrow, it could lead to an optical phenomenon called the ‘diffraction phenomenon’. Diffraction phenomenon causes an image to look less sharp.
This is what happened to the f/22 example here, which looks less sharp than the f/8 example.  Therefore, keep diffraction phenomenon in mind whenever you are considering a narrow aperture setting, especially with f-numbers over f/11. The best setting is one with good balance between diffraction and size of depth-of-field, which was achieved at f/8 for this example. 

 

Deep focus can help you achieve photos like this!

Shot with the EF24-105mm f/4L IS USM at 24mm, f/8

EOS 5D Mark III/ EF24-105mm f/4L IS USM/ FL: 24mm/ Aperture-priority AE(f/8, 1/400 sec, EV+0.7)/ ISO 100/ WB: Auto

A short focal length and narrow aperture to achieve deep focus
I used the deep focus technique to capture this image of the bow of a ship, with the sea in the background. Notice how the entire shot is in focus, from the foreground all the way to the back. The wide-angle end of the lens, with its short focal length, provided a large depth-of-field which made it easy to achieve deep focus.

 


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Digital Camera Magazine

A monthly magazine that believes that enjoyment of photography will increase the more one learns about camera functions. It delivers news on the latest cameras and features and regularly introduces various photography techniques.
Published by Impress Corporation

Tomoko Suzuki

After graduating from the Tokyo Polytechnic University Junior College, Suzuki joined an advertisement production firm. She has also worked as an assistant to photographers including Kirito Yanase, and specializes in commercial shoots for apparels and cosmetic products. She now works as a studio photographer for an apparel manufacturer.

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