Focus stacking is a process that combines technique (shooting) and processing (software) to dramatically increase the Depth of Field (DOF) in photographic images.  It is accomplished by taking multiple images of a single subject, each taken at different focal distances.  Those images are then aligned and merged together to produce a single composite image with an extended DOF.  Think of HDR photography, but instead of bracketing the exposure, you will be bracketing different focal points throughout the subject. 
 

When to Use Focus Stacking

Macro Photography

I love macro photography.  It is both challenging and exciting.  For me, the most challenging part of macro photography is keeping the entire subject in focus.  Focus stacking allows me to do this.
 

exposure and manual focus.  Set the aperture between f/8 and f/16 (or your len’s “sweet spot”.   Then set the shutter speed to capture the correct exposure.  If you are using a tripod, there will be no limits to how slow the shutter speed can go.  If you are shooting hand-held, you will have to maintain the minimum shutter speed necessary to avoid camera shake.

 

Two Photographing Techniques

There are two methods used for gradually incrementing the focusing distance in order to increase the Depth of Field.

1.  Moving the Camera:   This method is usually done in a studio where the photographer can have more control.  This method captures multiple focus points in the same image by minutely moving the camera between each shot, keeping the focusing point the same.  Since only a small portion of the image will be in focus in each shot, moving the camera closer between each shot allows you to move that small portion of focus through the depth of the image so that every portion of the image will be in focus in at least one of the shots.

In order to move the camera smoothly, it will be necessary to use either focusing rails or bellows.  I use the Adorama Macro Focusing, 4 Way, Fine Control, Camera Focusing Rail.  It allows me to move the camera in very small increments, without disturbing the camera.

StackShot from Cognisys Inc.  “StackShot is an electronically controlled macro-rail (focusing rail), that coordinates the movement of the rail and the triggering of the camera.” 

2.  Refocusing:  In this method, instead of moving the camera, you refocus the lens on different portions of the subject to get the entire subject in focus.  This method usually involves taking three to a dozen or more images.  This method allows photographers to use Focus Stacking while just using a quality camera and a sturdy tripod, and still get excellent results.

Start by focusing on the nearest point of the image that you want to be in focus.  For the next shot, being as careful as possible, adjust the focus on your lens to focus a little deeper into the image, and take the shot.  Keep doing this until you have captured all parts of the subject that you want to be in focus.

The depth of the subject, the magnification used and the aperture setting all go into determining how many images you need to shoot in order to make sure you have the entire subject in focus. 

Regardless of which method is used (moving the camera or refocusing), the entire image is enlarged, or made smaller, depending on the direction of your focus or the direction you move the camera.  As a result, all of these individual images will need to be aligned before they are merged together.

Whichever photographing technique you use, you need to make sure that the images are taken in sequence.  Shoot from the back to the front, or visa-versa, but if you go out of order the software won’t be able to blend the images together properly.

There are several software programs you can use to align and merge multiple images together and the methods used by each are all very similar.  Photoshop CS4 and CS5 both do this very well.  Other programs to consider are: Helicon Focus, CombineZM,  Zerene Stacker, and TuFuse.

Not only are there several different software programs to focus stack images, but there are several methods within each.  In Photoshop CS5 there are several different combinations of steps to accomplish the same end result.  I will describe two methods in this article, but there are several other methods, including using Photoshop Lightroom.
 

How to Align and Merge Images for Focus Stacking

For my first example, I had taken a total of 20 images of the same orchid for merging.  I used a focusing rail and started by focusing on the part of the orchid that was furthest from the camera.  Then I moved the camera further and further away from the flower in about 1/16^th inch increments, until I had all of the areas of the flower in focus up to the closest area from the camera.  At this point, you will have moved your camera approximately 1 ¼ inches in total from the first shot to the last shot.  I did not refocus each shot as I moved the camera.
 

For the example below, I am only using six of the 20 images I shot to make it easier to follow along.

© 2011 Brad Sharp.   All rights reserved.

The next 4 partial images depict the sharp and blurry portions of the orchid from the first photo shot and the last photo shot.


© 2011 Brad Sharp.   All rights reserved.

EXAMPLE 1 A
Image 0665 (first image shot): This is the portion of the orchid that was the furthest away from the camera.  Notice you can see the detail on the orchid.
 

© 2011 Brad Sharp.   All rights reserved.
 

EXAMPLE 1 B
Image 0685 (last image shot): As I moved the camera further and further away, and focused on the areas of the flower closest to the camera, the area of the orchid that was furthest away in my first shot is no longer in focus.

© 2011 Brad Sharp.   All rights reserved.

EXAMPLE 2 A
Image 0665 (first image shot): This is the portion of the orchid that was the closest to the camera in the first image. Notice that unlike the portion of the orchid in Example 1 A, this portion of the orchid is blurry.
 

© 2011 Brad Sharp.   All rights reserved.

EXAMPLE 2 B
Image 0685 (last image shot): This is the portion of the orchid that was the closest to the camera in the last image. Notice that unlike the portion of the orchid in Example 1 B, this portion of the orchid is in focus.

Method One: Photomerge

1. Open Photoshop Bridge in CS4 or CS5 and select the images you want to use.
 

2. Open Tools ->Photoshop -> Photomerge

The Photomerge box will open up…

© 2011 Brad Sharp.   All rights reserved.

If you look at only one of the layers it will look something like this…  It is because the program determines which portion of each image is in focus and only keeps that portion.
 

© 2011 Brad Sharp.   All rights reserved.

 

9.   Now select Layer ->Flatten Image.

© 2011 Brad Sharp.  All rights reserved.

Now you are ready to edit the image like you would with any other image, such as cropping, adjusting levels, etc.

This is the final image, where the entire flower is in focus, including the hood and pouch (my scientific terminology), while the background is slightly blurred.

 

© 2011 Brad Sharp.   All rights reserved.