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.
Additionally, if you would like to know how to create a focus-stacked image, read this article Focus Stacking in Photoshop.
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 drop 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.