When shooting macro photography, it is often nice to get the entire subject in focus but leave the rest of the image with a beautifully out-of-focus bokeh. This is where "focus stacking" helps. Focus stacking involves shooting a series of images while methodically changing the focus point from the front to the back of your subject. The most accurate way to do this is to use a macro focusing rail, such as our B150-B.
The picture (left) was compiled from 6 focus-stacked images. The distance from the flower to the film plane was .5 meters (~ 20 inches), giving a reproduction ratio of 1:1.2 using the 180mm macro lens. From the front edge of the flower to the back edge was about 18mm (~ 3/4"), and using the B150-B the camera/lens was shifted 3mm (~ 1/8") closer to the flower between each shot (about 2 ½; rotations of the B150-B lead screw). The ideal number of images and the amount of shift between each image depends on the aperture selected, the focal length of the lens being used, and the camera-to-subject distance. Practice will help you find the right combination. Set the camera's exposure mode to Manual, turn off Auto White Balance (the sunny or cloudy settings are usually fine), and set focus to Manual.
A handy tip that helps in post processing is to take a throw-away image with your finger in the picture to mark the beginning of your sequence of shots and then again after your last shot.
After you have your series of images, it is time to process them. We like using Adobe Lightroom 4.0 and Photoshop 5 Extended. It is better to save post processing until after all your images are merged. There are several different methods to create a "focus stacked" image, but this process is one we found that provides the most control and is simple to follow.
- Import your photos into Lightroom (if you don't use Lightroom, you can use Adobe Bridge).
- Select your images, Command-click (or right click) on one of the highlighted images, float the mouse over the "Stacking" option, then click "Group into Stack". All the images will then be grouped visually behind one image.
- Command-click (right click) on the selected stacked images and then float the mouse over the "Edit In" option and click "Open as Layers In Photoshop...".
- After the images have all loaded, select all the layers in the layer panel and click Edit then "Auto-Align Layers...". Use the Auto option in the Projection box and click "OK". Depending on the file size this may take a while to render. It's a good idea to save your image as a new Photoshop File Document, preserving your original images.
After the layers have all been aligned, select all the layers again, click Edit, then "Auto-Blend Layers...". Select "Stack Images", make sure the "Seamless Tones and Colors" option is checked and click "OK." Again this process may take a while depending on the number of layers and your file sizes. Save again.
- Inspect your blended layers. Look for areas in your image that aren't in focus but should be.
- Starting with the layer that is lowest in the layer panel, Alt-click the eye (show/hide layer) icon to isolate that layer. Selecting the layer mask and use the Paint Brush to paint white to add the part of the image that is in focus or black to remove part of the layer that is out of focus and is covering an in focus sub-layer. Perform the same actions wtih all subsequent layers. Only edit the layer mask and not the image layer.
- To reduce file size, flatten image and then apply other post-processing as desired.