KO/4Photography: Tips for Depth of Field Control in Macro Photography

Depth of field is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph, it varies depending on camera type, aperture and focusing distance. If you are into photography you probably already know this and how critical it is when you photograph in macro distances.

This image was done with a 100mm macro lens with a life-size converter attached, at a distance of 4 inches to the object to achieve this type of magnification. The Depth of Field you see here is impossible to achieve, as there is no way to have the whole ring in focus with this focal length and this distance to the object.

Here are a couple of test shots to show a comparison between an f/8 and an f/32 exposure of this image:

In this particular image f/8 would give you a very shallow Depth of Field, so if you would like to have more then f/32 would seem to be a better choice, right? But if you take a closer look, you will realize it is just not that easy.

The magnified image shows you that f/8 has shallow Depth of Field but, because it represents the sweet spot of this lens, it gives you great detail in the focused areas. On the other hand f/32 gives you more Depth of Field, but it lacks detail overall.

This lack of detail is due to diffraction, that is the slight bending of light as it passes around the edge of an object giving the photographed image a soft focus effect. So, sharp focus and deep Depth of Field are impossible to achieve in this image due to optical limitations.

A great work-around for these limitations is Focus Stacking (also known as Focal Plane Merging, Z-Stacking or Focus Blending), which combines images photographed with different focus distances into one final image with a greater Depth of Field.

This technique is only possible if the camera, and all the elements on the image are perfectly still, so the use of a steady tripod is really important.

Another important factor is to shoot, and focus without touching the camera. In this particular image the camera was tethered with a computer and a remote shooting app was used to focus the image.

The best way to capture these images is to start by focusing on the closest area first, then keep shooting, making sure you cover all the focusing length (move focus farther away from the camera with each successive shot). Just use the controls of your remote trigger and app to fine-tune the focus for each shot.

The final number of shots depends on how detailed you want your image to be, but keep in mind that the more images you have, the harder it will be to process later on. This particular image was made with a merge of 21 images.

After the images are captured it’s time to process them. There are a lot of software options on the market for focus stacking; this image was edited with Adobe Photoshop CC. Here are the steps:

Open Photoshop, go on File > Scripts > Load files into a stack
Select all the pictures and turn on “attempt to automatically align layers”
Select all your files in the layer panel on the right side
Go to edit > Auto-Blend Layers and select “stack Images”

You will end up with a stack of layers with associated masks that look something like this:

Each layer mask reveals the best of each focused part of the image, and they can also be manually adjusted for more controlled results. The final images are usually very impressive and allow you to achieve effects that would be impossible to reach any other way.

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