DIGITAL PHOTOGRAPHY NEWS FROM ePHOTOzine

Optical distortion is something that affects all lenses to some extent. However, the effect is more pronounced in certain lenses and can be used to give a different spin on an otherwise 'normal' view of an object. 

Although it distorts images, it is not always a negative effect and it can be used in different situations to create abstract or more creative shots of subjects.

Below, we've listed what types of optical distortion there are and how they can affect your images, either in a negative or positive way. 

• What is Curvilinear distortion?
• What is Pincushion distortion?
• What is Mustache distortion?
• What is Chromatic aberration / purple fringing?
• What is Vignetting?

 

What is Curvilinear distortion?

This is where lines that should be straight in your image appear curved or bowed in some way. There a quite a few different types of this distortion, but the most common you will come across is barrel distortion, where vertical lines appear to curve outwards like a barrel. This type of distortion is most common in wide angle or fisheye lenses. The effect will be really pronounced in the fisheye as the effect is more deliberate here.

This can be used in portrait images to create unique looking images where the facial features are stretched and warped, this works equally well with humans and animals. 

 

 

 

What is Pincushion distortion?

Pincushion distortion is the opposite of barrel distortion, as the lines bow inwards. The effect is usually quite subtle and can only really be seen in square or rectangular objects when they are shot straight on, such as architecture with windows and doors, and other straight lines. This effect tends to be more of an issue in long telephoto lenses. Pincushion distortion is a lot less pronounced than barrel distortion and so it is often not noticeable in images unless you look really closely. However, it can also be corrected quite quickly and easily in photo editing software. The majority of modern cameras will provide built-in options to correct for this as well.

 

Extreme example of pincushion distortion, from an uncorrrected image, from the Sony E 18-105mm lens - you can see corrected versions in the review.

 

 

What is Mustache distortion?

Mustache distortion is basically a combination of barrel and pincushion distortion. Some lenses display both at the same time. It is most commonly seen in wide angle zooms and makes straight lines in images appear wavy. It can be noticed on the horizon, for example when photographing seascapes, particularly if the horizon is near the top or bottom of the frame.  

 

 

What is Chromatic Aberration?

Chromatic Aberration creates colour fringing on an image, usually around the lines and edges on the image, but it can also be present in other areas of the shot, where there are areas of high contrast, for example a black tree branch, against a bright sky. It usually appears as a purple, glowing halo giving "purple fringing", or can appear as red/magenta lines, often with green/cyan lines as well.

 

An example of chromatic aberration can be seen above, note the megenta and cyan / green lines on the edges of the window frame. You can see an example of purple fringing below, where the gravestone is up against a bright (blown out) sky. 

This can often be corrected either in camera automatically in modern cameras, or in photo editing software, such as Adobe Photoshop, and Adobe Lightroom.

 

Purple fringing can be seen around the top of the gravestone.

 

 

What is Vignetting?

All lenses have a little vignetting - it's the term used when the image is darker at the edges than in the centre, due the curvature of the lens. Vignetting can sometimes be used to your advantage as a stylistic tool, to highlight the main aspect of your image in the centre. Most modern cameras will automatically correct for vignetting, depending on the lens used, and this can be corrected in photo editing software quickly and easily, or alternatively added to give a creative effect and style to your photo. See our guide on how to add a vignette to a photo in Photoshop.

 

Severe vignetting can be seen in this image.

 

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Photo by Joshua Waller

 

Aperture is very important when it comes to portraiture as it controls how much of the background and foreground is in focus, which has an effect on how much of the focus is on the subject of your portrait. 

 

1. Depth-Of-Field

There is an amount of front and back sharpness in front of and behind the main focus point of your image and this is referred to as the depth-of-field.

The amount of depth-of-field within an image depends on several factors:

• The distance between the camera and the subject - The closer the subject the more shallow the depth-of-field. With distant scenes, therefore, there is plenty of depth-of-field.
• Choice of lens aperture - The wider the lens aperture (ie /2.8, f/4) the shallower the depth-of-field, and the smaller the aperture (f/16, f/22) the greater the depth-of-field.
• Focal length - Contrary to popular belief a wide-angle lens does not give greater depth-of-field than a telephoto lens if the subject magnification is the same. You can test this for yourself. Take a frame-filling headshot with a wide-angle lens (you will have to get close to the subject, so warn them!) and then do the same frame-filling shot with a telephoto – this means backing away from the subject. Use the same aperture for both and you will see that the depth-of-field is the same.

Some cameras come equipped with a depth-of-field preview button, letting you see how much depth-of-field you have before taking the shot, but you can just experiment with depth-of-field and preview the shots on-screen to see what works best if your camera doesn't have this particular function. 

 

Photo by Joshua Waller

2. Photographing People

In terms of portraits, especially outdoors, wider lens apertures are often best because they throw the background nicely out of focus. How effective this is depends on the scene and focal length as well as aperture choice. If your subject is standing quite close to a distracting background even shooting at f/2.8 or f/4 will not throw the background out of focus but bringing the subject forward a couple of metres should work nicely.

If you do use a wide aperture for your portraits, do make doubly sure that the subject's eyes are in focus. With the shallow depth-of-field created by wide apertures, even a small error can mean unsharp eyes and you do not want that in your portraits.

 

Photo by Joshua Waller

3. Bokeh Backgrounds

How the background is thrown out of focus depends on the lens. Bokeh is the term used to describe the pictorial quality of the out of focus blur. Lens design and aperture shape play a large part in how effective its bokeh is, so do try it with your own optics. A good test is shooting a close-up portrait outside against a background with some bright pinpoints of light, ie sun glinting off water, car lights, streetlamps etc.

Of course, you might prefer greater sharpness in your backgrounds and that is when small apertures are used. The important thing is to keep your eye on the background and if it looks messy or cluttered use wide apertures rather than small ones.

 

Photo by Joshua Waller

 

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To help you give your urban photography an abstract feel, here are 8 top tips on what, how and where to take your photos when out exploring a town or city. 

 

1. Focus On What's Interesting

When you find something that catches your eye, think about how you can compose the shot to take the subject away from its surroundings so it becomes abstract rather than a great city shot with several interesting elements. The key to capturing an image that works is to create an image out of something ordinary that you wouldn't normally see while still creating an appealing shot.

 

2. More Than One Point Of Interest

When you have a subject that has multiple points of interest you have the opportunity to capture various elements, some which may not have seemed so obvious as working in an abstract way at the start.

 

3. Create Scale

Just because you're capturing abstracts doesn't mean you always have to work up-close. Think of it as cropping out unwanted elements rather than using your lens to zoom in. Use surrounding elements to emphasise size but still frame the image so the building's surroundings are removed, giving emphasis to its shapes and patterns rather than it having context. 

 

4. Use Colour

By using a single bright colour in a shot that's mostly of the same shades can give the viewer of the image a point of focus that can also be used to guide and lead the eye to other points in the shot. This is even more so when the area is limited and contrasts so greatly with the rest of the image. Strong blocks of colour can also work well but you don't want one to overpower the other so the viewer doesn't pay attention to the rest of the frame. 

 

 

5. Look For Shadows 

This isn't something our eyes tend to see but when arranged in the frame properly, they can be a great subject matter on their own or enhance the shapes/patterns of an object you're making your point of focus. 

 

6. Lines Work Well

 If you want to use lines in your image, try to find a location that gives you a shot that has lines that vary in size and colour. Bolder lines can have more impact than small, faint ones and do remember they will still guide the eye through the shot and tell the viewer where they should be looking. Don't think lines have to be straight either as a curved line will still guide the viewer's eye. 

 

7. Shoot Through Other Objects

If you find a rain-covered window or even a water feature that can be used to capture a distorted reflection thanks to the ripples in the water, use them to your advantage. Keep an eye out for coloured glass, reflective buildings and any other items you think will give your city shots that abstract feel you're searching for. 

 

8. People Like Patterns & Symmetry 

As humans, we like to see repeating patterns and symmetrical objects so take advantage of this. Patterns can guide the eye across an image as well as make your abstract shot more interesting thanks to the shapes they create. 

 

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