The technique of focus stacking allows you to overcome one of the biggest problems with macro photography; the limited depth of field. Before I explain what focus stacking is, it may be worthwhile explaining what depth of field is first. I don’t want to delve into this subject in too much detail, because it demands a whole article in its own right, but I will try to explain it briefly. The images later in this article will do a better job of explaining it.
Briefly, the depth of field is the amount of image that is in focus. A camera lens can only focus on one particular spot of a scene, but the area in full focus will extend in front of and behind this single spot. The extent, or depth, of the in-focus area will vary according to the type of lens, the aperture setting and the composition of the scene. Exactly how all these variables interact with each other is beyond the scope of this article, but it is enough for you to understand that it is almost impossible to have all of the scene in focus when shooting in macro. To demonstrate this, take a look at the image above of the wildflower after a rain shower. You can see that the front of the flower is in focus, but the top and bottom of the petals drops out of focus and the background is completely blurred even though it was only a few centimetres back. This demonstrates a shallow depth of field and it is intrinsic with macro photography.
Therefore, it can be almost impossible to take a macro photograph that has full focus front to back in the final image. This is where focus stacking can be used. It involves a bit more time and post production work but the results often make it worthwhile. Focus stacking is a technique that is often used by product and food photographers and all of us have seen these images in supermarkets. So here is my take on a product shot that uses focus stacking to ensure full focus throughout the final image.
The product I chose was some pistachio nuts I had. I placed a few on a white background and fitted the Nikon 105mm macro lens onto my camera before securing it on a tripod. I took one image where I focused on the centre of the image to test out the lighting.
This one image is a good example of what would be expected of a normal macro photograph not utilising the focus stacking technique. You can see from the image that the middle is in focus but the bottom and top of the image is blurred. This image was shot with a small aperture (ƒ/16) and yet most of it is out of focus. Now let me describe the technique of focus stacking. In the next article I will describe how to employ Adobe Photoshop to produce a final focus stacking image.
The technique involves taking a serious of images where you manually shift the focus between each shot until you have focused across the entire scene. In this example, I would focus on the bottom of the scene first and take a serious of images where the focus would shift to the top. For this technique to work, the camera must be on manual focus. Focus at the bottom and take the image, then manually turn the focus ring on the lens a small amount to focus on an area just slightly higher up the scene and take the next image. Repeat this process several times until you have taken an image where the very top of the scene is in focus. For my example, I took a total of 11 photographs. Once I had taken all my images, I imported them into Lightroom before opening them in Photoshop to produce the stacked image you can see below.
You can see that the resulting image has a sharp focus throughout. I will post detail instructions on how to achieve this effect in the next article. In the meantime, what do you think? Is focus stacking a technique that you would try or have you already tried it? Would it be useful?