What is focus stacking and how to do it?

Focus stacking is an image-combining technique that aims to increase the depth of field of a photograph. Simply put, a sequence of images is taken, each at a different focal depth, and merged together using software. While none of those images will focus our subject totally, the sequence should contain all the data needed to generate an image in which the subject looks sharp.

The principle of stacking is no different than that of HDR (High Dynamic Range) photography, except that the idea here is to increase sharpness rather than dynamic range. This technique is particularly useful in macro photography, where the depth of field is often very small.

▌Image taken using focus stacking technique. 8 camera-stacked photos taken with an **Olympus Zuiko 60mm f 2.8** macro lens.

Advantages of focus stacking

Focus stacking offers great flexibility as it allows you to capture images always taking advantage of the so-called “sweet spot” of your lens, which is usually between f/5.6 and f/8. It also makes it possible to generate images with different levels of depth of field.

The focus stacking technique offers results that are physically impossible with traditional techniques or equipment, and is very popular in macro and commercial photography and in scientific microscopy work.

How to do focus stacking

While the principle may sound complex, the focus stacking technique is actually quite easy. The starting point is to identify a subject from which different images can be taken for later stacking. Due to the nature of this technique, these images must always be taken from the same perspective. Therefore, our subject must be static and in practice we will almost always work indoors: wind or the movement of the subject can make it difficult to accurately merge the images. Water drops, flowers and plants are good subjects for our first attempts.

Once we have decided on the image we want to achieve, we will take the sequence of photographs to be stacked starting from the front of our subject and gradually moving back the focal plane from there. There are lenses and cameras that allow this process to be automated, but if we do not have one we will have to focus manually using a focus rail.

A sequence of three or four images can be enough, but it is generally recommended to take more than 10. In any case, this number will depend on the subject, the aperture you are working with, the reproduction ratio and the formal results you want, but it is always better to err on the side of taking too many images than taking too few.

Once you have your sequence, you will need the appropriate software to align and combine the images. As we said, some cameras can do this themselves, but if you don’t have one you can use Photoshop or specialized free applications, such as CombineZM, Helicon Focus and Zerene offer more functions, but you have to pay to download the full versions.

Batteries: Don’t forget them

The focus stacking technique, as well as the continued use of the flash, causes our batteries to discharge quickly, so it is essential to have a good supply. In projects that require taking dozens of photos over many minutes of work, the best solution may be dummy batteries connected to an external battery. This system will prevent us from running out of power in the middle of the task and, surely, having to start over (related: Batteries and chargers for cameras: all models, original and clones).