Focus stacking boils down to the practice of taking multiple images at several different focusing points across the subject and “stacking” them together in software to create an image with perfect focus front to back that would have been impossible to create with just a single image (or using front tilt as in a view camera at 150MP resolution). This technique is particularly useful for macro subjects, but it can also be used in landscape, still life, or for essentially any non-moving subject. Phase One's built in Focus Stack Tool for the XF Camera system is perfect for putting this technique into practice in a predictable, repeatable way.
Using a focus stack to capture an image is ideal for medium format camera systems since their high resolution sensors render everything, including out of focus areas, so well. As resolution increases acceptable sharpness decreases. The more resolution you add, the better you can render the not-perfectly-in-focus areas in an image, effectively reducing the amount of overall sharpness. Focus Stacking helps alleviate this habit of physics. While certainly not necessary for all types of images, macro and still life photographers will especially appreciate the automated Focus Stack Tool, though landscape and architectural photographers may also find the built in Focus Stack Tool in the XF body an extremely welcome feature.
How To Use The Focus Stack Tool
The Focus Stack Tool is a simple one to use, but it’s important to have a few things straight before you jump right in. You’ll need an XF camera body and any Phase One IQ series digital back (IQ1, 2, 3, and 4 are all compatible). First, you’ll want to have your subject in front of the camera, obviously. You’ll also want to make sure you have autofocus turned on. Next, you’ll want to have all of your exposure settings dialed in. If you’re using strobes, make sure they are ready to fire. Something to consider here as much as possible is your aperture.
Choosing The Appropriate Aperture
It’s important to remember that focus stacking doesn’t add sharpness. The final image will only be as sharp as the “in-focus” area of one of your images. Since you’re going to be stacking your images, there isn’t a need to shoot with the smallest aperture your lens will give you since that will introduce softness due to diffraction. You could stack those images, but the final image would be equally soft front to back. Also, just because you can shoot a focus stacked image with a wide open aperture and achieve a final “in-focus” image, doesn’t mean you should. Shooting at a wide open aperture will result in several more images taken and stacked, adding unnecessary strain on your machine. Plus its not very often that a wide open aperture is your lens’s sharpest option.
Once you’ve made the decision to focus stack an image you’re no longer using aperture for depth of field, you’re using it for sharpness. That being the case, for the best image quality, choose the sharpest aperture your lens can give you, like f/8 or f/11. If you don’t know what the sharpest aperture is for the lens you’re using, take some test images with equivalent exposures at different apertures. Chances are it’s In the middle of the lens between f/5.6 to f/11. Remember, don't worry about depth of field.
Navigate to the Focus Stack Tool On The XF
The Focus Stack tool can be found on the XF body’s top touch screen by swiping left through the available tools.
The numbers you see on the left hand side of the focus stack tool are called MCUs, or Motor Control Units. These units are used in conjunction with the camera’s autofocus motor to determine a spot in the motor that relates to a point in space. By assigning an MCU to a near and far point, the XF body will understand how many images it should take automatically in even intervals to create a focus stack.
Initiate Live View
Now you can initiate live view on the digital back, or better yet, tether into Capture One and initiate live view there. This step is not required, but it is highly recommended, as this is how you will determine the exact beginning and end points for the Focus Stack Tool to create the stack, so precision is key.
Tip: Turn on the Focus Mask tool in Capture One or on the IQ4 150 to find focus easier
Select The Near Point
The front and rear scroll whees are used to change the MCU. The front scroll wheel next to the shutter release will adjust MCUs by 1 digit, while the rear scroll wheel changes MCUs by 10 per click, so use the rear scroll wheel to get in the ballpark of where you want to be, then use the front scroll wheel to refine. As you use adjust the MCU you’ll notice the mounted lens come alive and adjust focus. Change the MCU using the scroll wheels and look at the live view feed at the same time. Find the point in space closest to the camera you want to be in focus. It may take some trial and error to find it. Zoom into the live view feed to confirm. Once you find the “near point” you want to be in focus, push the bottom silver button on the XF body next to the flower icon and a floppy disk (classic). You should see the same MCU in small digits next to the flower and disk icon as the large MCU to the left of the tool. The near MCU has been saved.
Select The Far Point
Repeat the above steps to find the far point. Once you’ve found the right MCU for the far point, click the top silver button on the XF body next to the mountain icon.
Make Final Adjustments
Most blue ring lenses give the XF body the ability to automatically suggest a number of images to take in a stack, which is located in the bottom left of the Focus Stack Tool. If the number is blue, then the XF body has calculated this number automatically based on your chosen aperture, the distance between the near and far points currently selected, and the optics of the lens currently attached. If this number is white, then you will need to manually tell the camera how many images to take in a sequence by using the far left scroll wheel (typically the ISO wheel). In general, the more images you take in a sequence, the better. This gives the software more images to use in the stack and will result in a cleaner stack. The automatically generated blue number is the camera’s opinion for an optimal stack, but if you would like, you can manually change the automatically generated number by going into the advanced section of the tool in the top left corner, just under the X icon.
This section provides advanced options, like changing the automated stack recommendation mentioned above by adjusting the Image Count option. This is also where you can create a delay in between images, which is especially useful if you’re using strobes that need a few seconds to recycle. Lastly in the advanced menu, you can opt to use the electronic shutter throughout the stack, even if you haven’t set the XF to use the electronic shutter in normal shoot, however this is not recommended if you’re using strobes.
Initiate The Stack
At this point you’re ready to begin the focus stack. The urge to hit the normal shutter button will be strong, and you probably will a few times when you’re first getting used to the tool, but pressing the shutter button will not initiate the sequence and will instead take you back to the XF’s main menu. Instead, you’ll want to press the button on the back of the camera body just below the aperture icon, in between the scroll wheels. Many of the XF body’s tools are manipulated by the nearest button to a given icon, like the button just below the aperture icon in the Focus Stack Tool. Once this button is pressed while in the Focus Stack Tool, the sequence will begin.
A focus stack in progress with a 3 second delay for strobe recycle
Sit Back and Relax
The XF body will begin the focus stack and take a series of images focused at different but even intervals across the subject. The icon on top of the XF body will display the number of images left in the sequence at any given time, as well as where in the sequence the system currently is.
Import Images Into Capture One
If you haven’t been tethering it’s now time to import the images into Capture One. Once the images have been imported, you’ll notice a small icon in the bottom left of the thumbnails from the focus stack in the Capture One browser. This is because the XF body writes a small piece of metadata into each of the images taken in the focus stack, letting Capture One know that each individual image is part of a larger stack. To select all of the images from the stack at the same time, simply right click one of the thumbnails and choose Select By Same > Sequence ID XXXXXXXX.
Apply RAW Adjustments
When it comes time to stack the images you’ll be outputting Tiff or JPEG files, so now is the time to apply any RAW adjustments like highlight or shadow recovery, color correction, etc. Naturally any adjustment you make to one image will need to be made to other images as well, so its best to choose one of the images to work on start to finish, then copy and apply those adjustments to the rest of the images. Don’t worry about heavy pixel moving or retouching, as this will be easier to do once the final focus stack is complete and you can focus on that one final image.
Edit With Helicon Focus
After you’ve made your RAW adjustments its time to export into your focus stacking software of choice. We highly recommend Helicon Focus, as it highly effective and also has a plugin for Capture One Pro. To export into Helicon Focus, right click one of the thumbnails from your stack and click Select By Same > Sequence ID, selecting all of the images in that particular stack simultaneously. Right click one of the thumbnails once more and select Edit With > Stack in Helicon Focus. If you do not see this option then you do not have the Helicon Focus Plugin. Get it here.
After clicking "Stack in Helicon Focus" you will choose the output file types for the images being sent to Helicon Focus. Helicon Focus is not able to stack Phase One RAW files, so you will need to choose to output JPEGS or TIFFs. After some processing, Capture One will automatically bring up Helicon Focus for you to begin your focus stack. Using Helicon Focus is fairly simple, but instruction in how to do so goes beyond the scope of this post. For more information on Helicon Focus and to download it for the first time, click here.
Have questions? Let us know in the comments. Happy stacking!