Have you ever wondered how landscape photographers get those beautiful images, the ones where the shot is in focus from the foreground to the horizon? There are a number of techniques that they can use to achieve this: wide-angle lenses, very small apertures and—one relatively obscure technique—focus stacking.
What is focus stacking, and why would we use it?
Put simply, focus stacking is a way of increasing your depth of field by shooting multiple images. Each is focused on a different point in the image and then combined using Photoshop. There is a very simple reason that we might do this, and that is diffraction.
Diffraction is a problem of the digital photographic age. In layman’s terms, it is caused when the angle of the light hitting the sensor’s pixels becomes too acute. This is usually at around f/8-11 on APS-C sensor cameras, and f/11-16 on full frame cameras. The end result is that, if your aperture goes beyond this diffraction limit, there is a noticeable softening of the image. This is a problem for photographers looking to get a deep depth of field. Let’s take a look at how to achieve a focus-stacked image.
The most common use for focus stacking is in landscapes and macro work. In either case, the http://photographytricks.com/a-brief-guide-to-cleaning-dslr-sensor/shooting technique is the same. You will need to shoot several images with the focus points overlapping. The most important elements that you will need are: 1) a tripod and 2) consistent light. If the lighting is constantly changing, it will be difficult to efficiently blend the shots together. The use of a tripod is required because the position of each individual shot needs to be identical. It is only the focus that we are changing.
The first image should be shot with the focus point set to just beyond the nearest point that you want in focus. This is to account for the depth of field that the set aperture will give you. The second shot should be focused just before the midpoint of the scene, making sure that there is some focus overlap with the first shot. The third image should be focused about two-thirds of the way into the scene, and the last shot just back from the infinity point, again using the depth of field to expand the focus all the way to the horizon.
Depending on the scene, you should consider three shots the minimum, but shoot more if required. For example, a macro with intricate details might require a higher number of shots as in the example we are using in this tutorial.
When shooting, make sure your light remains constant and that your exposure also remains the same. Use the same shutter speed, aperture and ISO. If you normally shoot with auto ISO, reset it to a suitable manual setting.
A Sequence of six images will be used to create our shot in this tutorial.
Creating the image
Creating a focus stack in Photoshop is not too difficult. You will need Photoshop CS3 or later.
With Photoshop open, from the menu select File – Automate – Photomerge. Browse for the images that will make up your focus stack, then click ok. You can also open all the images in Photoshop and then select Open Images.
The Photomerge dialogue
In the Photomerge window, deselect the Blend Images Together checkbox at the bottom, and make sure that Auto is selected from the Layout on the left. When ready, click the OK button, and Photoshop will begin to align and blend the images. Depending on the power of your computer, this might take a few moments to several minutes. Once it has completed, the new image will open and you will see from the Layers palette on the left that there is a layer for each individual shot used.
Because, when you change focus in a shot the image size changes very slightly, there is one more step we need to do to finalize the image.
You can browse or use already open images
The six images layered together
Select all the layers in the Layers palette. From the menu, go to Edit – Auto-Blend Layers. A small window will open. From it, click the Stack Images checkbox. Then click OK. Photoshop will now make minor adjustments to the layer sizes, aligning them to counter the focus shift.
When this has completed, you might find that you need to crop the image slightly, as there may be some canvas area or some softness showing around the outside.
Photoshop will automatically blend the images
When satisfied, you can merge the layers and save the image.
The final result: a macro image shot at f2.4, in perfect focus front to back
Focus stacking is an excellent tool for countering the diffraction limit of our sensors, particularly when shooting macro or landscape shots. With care given to using a locked-off tripod and even, unchanging light, you can get beautiful, sharp images with an immense depth of field.