About this image: I used a telephoto macro lens (100mm) with the aperture wide-open (at f/2) to create this selective focus image of a white daisy.
There are many ways to be creative with photography and post-production. One creative control relates to exposure settings: By controlling the aperture used to make an exposure, the photographer can determine how much of the subject—and which areas—are in focus in a photograph.
This article discusses the creative use of aperture controls with an emphasis on using aperture for creative selective focus. The good news is that apparent focus can be manipulated after the fact in post-production. So, if you didn’t get selective focus right in the camera, all is not lost! I will show you several effective techniques for managing selective focus in the Photoshop darkroom.
The Exposure Triangle
The three variables within an exposure are shutter speed, aperture, and ISO.
Shutter speed refers to the duration of the shutter—in other words, it is the amount of time the shutter is held open to let light into the sensor. From a creative viewpoint, shutter speed is primarily used to determine how motion is rendered.
ISO stands for sensitivity. You use ISO to increase or decrease the sensor’s sensitivity to light. The higher the ISO, the more noise will appear in an image, although this is becoming less of a factor with modern digital cameras. Note that increasing the level of noise in an image can itself be a creative effect utilized by the photographer.
Aperture controls the size of the opening in the lens. While a number of factors impact depth-of-field (the range of distances from the camera that is in focus) with a given camera sensor and focal length lens, aperture controls depth-of-field. Combined with the camera position, depth-of-field will determine which parts of your image are in focus, and which are not. As such, manipulating aperture is one of the most important tools available to the photographer.
Modifying Exposure to Use Aperture Creatively
Once you find the right exposure for your photo, you’ll need to use the exposure triangle to keep the camera settings balanced. So, if you modify one of the “legs” of the exposure triangle—-shutter speed, ISO, or aperture—you will need to change one or both of the other two “legs” to compensate.
Another way of thinking about this is to use the exposure triangle creatively. The job of the photographer is to pick the most important exposure setting; then the other settings in the triangle work around that initial choice.
For example, with the rear view shot of the white daisy shown below, I knew I wanted to capture the flower against a wildly out-of-focus background. I therefore opened my lens all the way up to its maximum aperture (f/2). Since this would generate an image with very shallow depth-of-field, I knew that I needed to position the camera so that it was as parallel as possible to the flower. Since the creative aperture that I selected was f/2, I set the other exposure triangle “legs”—shutter speed and ISO—accordingly to make sure the exposure was in balance.
In this shot, I lined the focal plane of the camera up to be as parallel as possible with the flower, and used a wide-open aperture (f/2).
Selective Blurring in Photoshop
You don’t need to worry if you don’t get the selective focus effect you are going for in-camera! It’s really quite easy to add a sense of selective focus using Photoshop, although it is important to do this with a light touch.
A number of filters that will blur your image are available on the Photoshop Filter > Blur menu. The two that I use most often are Gaussian Blur and Lens Blur (although I encourage you to experiment with the other blurs as well).
For instance, if you decide to use the Gaussian Blur filter (Filter>Blur>Gaussian Blur), you’ll see that the Gaussian Blur dialog box has a single control, Radius. The higher the Radius, the more blur.
With the Gaussian Blur filter, the higher the Radius, the more blur.
The trick is to apply the Blur filter selectively to an image. In order to do this, first duplicate the layer that you want to apply the blur to, and then make sure that duplicate is at the top of the layer stack in the Layers panel. Apply the Blur filter you want to use in the image to the duplicate layer. At this point, the entire duplicate layer will be blurred (which probably isn’t the effect you are going for!), and this blurred layer is what you will see in the image window.
Next, use this duplicate layer to selectively add the blur effect you want. Here’s how: Add a black Hide All layer mask to the duplicate layer and use the Brush Tool loaded with white to gently paint in the blurred area. Along with painting on the layer mask to control where the blur is applied in the image, you can also lower the duplicate layer’s opacity using the Layers panel to control how much blur is applied.
The photo below shows the winning team in a Fourth of July tug-of-war between the small beach communities of Bolinas and Stinson Beach, California.
I wanted to isolate the winning team members from the background, so I applied a Gaussian Blur with a Radius of 4.2 Pixels to a duplicate layer of the entire image. I used Gaussian Blur because this would probably look the most natural in a situation with a moving crowd behind the winning team.
I always apply the blur filter to a duplicate layer so I can adjust the opacity of the effect after application.
Next, I added a black Hide All layer mask (shown below as an alpha channel) to the duplicate layer and used the Brush Tool loaded with white to brush in the blur into the background, making sure that the blur wasn’t applied to the team members.
The Layer Mask I used with the Gaussian Blur, shown as an alpha channel.
Finally, I took the opacity of the duplicate blurred layer down to 27%, so the background blur is barely noticeable. The finished image, after converting it to monochrome, is shown below.
In the finished image, the background blur looks natural yet focuses attention on the team members.
The Lens Blur filter gives you more flexibility than Gaussian Blur, and tends to look more natural in situations where the blur would come from being out-of-focus, rather than from motion.
With an image of a daffodil below, my idea was to present the center of the flower in focus with the petals blurred. Once again, I duplicated the Background layer so that I could apply the Lens Blur to the duplicate layer, and then selectively brush in the blur.
With Lens Blur, there are a number of sliders to play with, but bear in mind that the primary control is once again set by the Radius: the higher the Radius, the more blur.
The Lens Blur filter provides a number of controls that allow you to mimic the way lenses create blur in-camera.
Since my idea was to have the center in focus, I added a white Reveal All layer mask to the image, and then used the Brush Tool loaded with black to paint out the blur at the center of the flower, so that it would stay in focus.
With this image of a daffodil I wanted the center to be sharp, and the petals to seem out of focus.
The daffodil layer mask, shown as an alpha channel.
The finished image shows the center of the flower perfectly crisp and in focus, with a slight—and very authentic looking—blur on the petals.
The finished Daffodil image shows a center that is crisp and in focus, and petals that seem slightly blurred.
Using FocalPoint to Alter Focus
FocalPoint is a plug-in that runs with Photoshop, Lightroom, Aperture, and Photoshop Elements. It is available for download for about $100 from onOne Software at http://www.ononesoftware.com/products/focalpoint/ (a free trial version is also available). FocalPoint is also available as a component of onOne Software’s Perfect Photo suite.
When I shot the image of the north spire of Notre Dame, shown below in Adobe Bridge, I used a moderate aperture (f/7.1) to try and create an out-of-focus background to differentiate the spire from the cityscape of Paris in the background.
The RAW captures of the north spire of Notre Dame shown in Adobe Bridge.
Looking at the image after opening it in Photoshop (below), I could see that the background was slightly out-of-focus, but not as much as I wanted. The dynamic post-production focus controls in FocalPoint were just what I needed to adjust this.
The background is slightly out of focus, but not sufficiently differentiated from the spire.
FocalPoint uses a so-called “FocusBug” control (shown below) to let you position the focal plane in three dimensions by dragging the end points of the controls to create a rectangle that is in-focus.
The FocusBug control allows you to manipulate the point of focus.
The parts of your image that are not in focus can be adjusted using FocalPoint’s Blur controls.
FocalPoint controls give a great deal of control over the quality and quantity of the out-of-focus blur.
FocalPoint provides controls—such as a brush—to apply its focus effects selectively. Note that my recommendation is still to apply FocalPoint to a duplicate layer in Photoshop if possible, as this will give you the most absolute control over the application of FocalPoint’s blur control via Photoshop’s layers, masking, and layer opacity.
I applied the FocalPoint focus manipulation to a duplicate layer so I could control its impact precisely with a Photoshop layer mask.
The Layer mask I used with the FocalPoint focus adjustment, shown as an alpha channel.
The final version of the image of the north spire of Notre Dame (below in monochrome) shows the excellence of FocalPoint’s focus modeling. In conjunction with a Photoshop layer mask, I was able to control focus so that the tower was crisp, but the background was subtly out-of-focus. I challenge anyone to visually distinguish this out-of-focus post-production look from an out-of-focus area attributed to the camera and lens.
The finished image of Notre Dame’s spire shows an out-of-focus background that is very hard to differentiate from an out-of-focus effect generated in the camera.
Aperture plays a key creative role in photography because together with sensor size, focal length, and camera position, it determines how much is in focus with the depth-of-field. If you can’t get the exact creative focus effect you want in-camera using aperture, it is possible to simulate selective focus in the Photoshop darkroom using a Blur filter. The FocalPoint plugin from onOne Software takes this a step further, and lets you resize the FocusBug control to precisely indicate areas that are in focus.
In this column I’ve explained:
The Exposure Triangle and how the interrelationship between shutter speed, ISO, and aperture works
The importance of using aperture creatively to determine selective focus
Using the Gaussian Blur filter
Using the Lens Blur filter
Applying the Blur to a duplicate layer, and using a layer mask, the Brush Tool, and layer opacity for greater control
Using the FocalPoint selective focus plug-in
About the Author
Harold Davis is an award-winning professional photographer whose work is widely admired and collected. He is the author of many bestselling photography books including the forthcoming Monochromatic HDR Photography, and his popular workshops are often sold out. Harold Davis is a Moab printmaking Master.