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What is focus stacking and why use it?

Focus stacking is a technique which consists of taking a series of photos, of the same subject, with the same frame and with different focuses. The advantage of this technique is to make your images much sharper and virtually obtain a greater depth of field. Focus stacking is mainly used for macro photography, advertising photography or landscape photography. One of the constraints in macro photography is the shallow depth of field. The goal is to succeed in focusing on all the desired elements of the scene. Even with a small aperture like f/22, you won’t be able to have complete sharpness when photographing a subject up close. This is called diffraction and it results in a loss of sharpness (blurring in the image). The solution: focus stacking. This technique makes it possible to reproduce a subject in detail while preserving perfect sharpness over the entire scene. In this article, we will see what focus stacking is and how it will give you both great depth of field and perfect sharpness.

Why use focus stacking?

Focus stacking therefore consists of merging several shots of the same subject, shifting the focus each time to obtain a final image with great sharpness and great precision in detail. Used in macro photography, product photography (packshot) and landscape photography, focus stacking can also be very useful for proxi photography. Proxiphotography or “close photography” is the set of photographic techniques allowing you to photograph small subjects without reaching macro photography. In this case, we often speak of a close-up.

This is an essential technique when you want to obtain great clarity in a scene where the foregrounds are too close together. Focus stacking therefore allows you to obtain a depth of field that would be almost impossible to obtain with a single photo.
Create a sharpness of different shots that would be difficult to achieve with only the functionality of your camera and the lens. Thanks to focus stacking, you optimize the efficiency of your lens (between f/4 and f/9 for better sharpness).

Shooting technique for focus stacking

The idea is to take a series of photos with the same framing while having different focuses. Then stitch these images together to merge them in post-processing. To facilitate the merging of images and therefore their alignment in your editing software, ensure that the foreground moves as little as possible. The framing must be identical as well as the position of the elements of the scene.

After adjusting your framing and exposure, start by focusing the foreground so that it is sharp.
Then image after image, you will gradually change your focus to make your depth of field evolve to the background. In other words, the foreground is sharp in the first photo and the background is sharp in the last photo.

Focus stacking and depth of field

Reminder: depth of field is defined by the sharp area of ​​your image. It varies depending on three elements:

Focal length: the longer the focal length, the more the depth of field decreases
The distance of the subject from the background: the closer the subject in focus is to the camera, the more the background is blurred. As you get closer to the subject, the depth of field decreases. Therefore, in macro photography, you will have to close the diaphragm of the camera as much as possible.
The opening of the diaphragm:

  • the aperture is open (f/2.8, f/3.2…), + the depth of field is small = little sharpness
  • the diaphragm is closed (f/16, f/18…) + the depth of field is large = lots of sharpness. In other words, the focus is on a larger area of ​​the photographed scene. Use soft spot mode and lower the ISO since your camera is placed on a tripod.
    In low light situations, the aperture will be even larger and the depth of field will be even smaller.
    This amounts to having a correctly exposed photo with elements of the scene in focus in the foreground, but not in the background. If you lower the aperture of the diaphragm (f/18, f/22, etc.), you risk having a bad exposure. You can then move away from the subject provided you have a focal length that can frame up close! The best solution lies in focus stacking.

Focus stacking in practice

Use a tripod (robust and stable) and a remote control (to avoid camera shake when shooting): your shots must be identical. If you bump your tripod even slightly, you can start again!
Have a standard or macro lens
Set your camera with an aperture like f/4 or f/5.6 to enjoy good sharpness and have nice bokeh
Use manual mode (to keep settings between shots) and manual focus
Take several photos (between 5 and 20) with different focuses (gently vary the focus ring or use the different focus stops on your camera): start by focusing on the most visible details. closer to you (foreground), then a focus on the middle plane. Finally, focus on infinity (background).

Focus stacking in post-processing

Recommended software: Photoshop, Affinity photo, Helicon Focus, PhotAcute, Zerenne Stacker…
Recommended image format: Raw (you can also do focus stacking in Jpeg)
Import your photos into Lightroom (to develop them): develop / synchronize. Tip: apply a preset (pre-defined parameter) to facilitate the process of processing your images
Export your photos to Photoshop: in Lightroom: photo / open as layers in Photoshop
Select all of your photos: CTR + A or CMD +A
Align your photos: automatic layer editing/alignment
Stack your photos: editing / automatic layer merging / stacking images
Export the photo (merged)
Use masks to correct any imperfections
Re-import your Photoshop file (.psd) into Lightroom to adjust exposure, saturation, etc.
Exporting images with a 20MP camera will take approximately 5 seconds per image.