All Photos Courtesy of Ben Grelle
One frustrating aspect of macro photography can be shallow depth of field. When working at such close distances you may only have millimeters of your subject in focus despite a tiny aperture. Sometimes this looks very cool and having that shallow depth of field adds an ethereal effect to your image.
Other times it just looks like you couldn’t get everything in focus.
A method to solve this problem is called ‘focus stacking’. This is a technique in which you take many pictures and use software to combine them, giving you a completely in-focus macro image.
Think of a loaf of bread. Let’s pretend that your camera is only capable of capturing one slice of bread in focus. Every other slice is blurry.
Macro focus stacking allows you to take an image of each slice…
…and then combine them into a fully focused loaf of bread.
The ‘slices’ of focus are obtained by starting at the front piece of bread, moving your camera forward, getting the next slice in focus, and continuing this process until you reach the final slice of bread.
Capturing Your Slices
How do you get the slices of focus? There are three main options.
- A macro focusing rail
- Helicon Remote
A macro focusing rail is a device that sits on top of your tripod and allows you to scoot your camera back and forth in tiny increments. Not only is it great for focus stacking, it is a must-have tool for serious macro photographers.
As it applies to stacking, it is a more manual option. It is not the most accurate, but it can certainly get the job done if you have a fine touch. You start by getting the front ‘slice’ of your subject in focus. Take a shot. Then slowly turn the wheel forward just a fraction and take another shot. Repeat until you reach the farthest part of your subject.
One issue you will find is that you don’t really know how far to move your camera forward with each shot. There are focusing rails that have rulers on them and if you do some depth of field (DOF) calculations, you can figure out how far to move forward with each shot. HOWEVER, in my experience, it is usually just easier to turn the knob on the focusing rail in very small, consistent lengths. You may have to take 20-40 images per stack, and trying to precisely move your rail in millimeter increments between each shot is a hassle. It’s best to just to do the smallest increments you can, and then throw out images you don’t need later. If the movement is shorter than necessary, it won’t harm the final stack.
The second method for getting focus slices is a software option called Helicon Remote. This is a special application that takes advantage of your camera’s autofocus mechanism. Your lens has minimum focusing increments. They are precise and uniform. Helicon Remote allows you to pick the first slice of focus, the last slice of focus, input the type of lens and aperture, and then it will calculate how many focusing intervals you need between each shot. Basically all you have to do is tell it where the depth of field is, and it calculates the rest.
The advantage to using software is that it is very precise. You are essentially tethering to your computer and you can live view your focus on a large display. The disadvantage is that tethered shooting can be plagued somewhat by bugs. While I admire this program a great deal, I have had to redo many stacks due to the program freezing up. Also, using your lens’ autofocus intervals means that you are not changing the distance of your lens to the subject. You are slightly changing the focal length to acquire the desired focus. This can introduce slight distortions and focal length compression. Many macro purists prefer a solution that allows them to keep the focal length absolute, and only change the distance to the subject to acquire their focus slices. The last disadvantage is that you cannot use manual focus lenses.
The last solution is a very clever piece of hardware called a StackShot.
This is an automated focusing rail that allows you to input your depth of field and moves your camera along the rail for you. This device is extremely precise and can give you some amazing stacks. The downside is that you have to calculate the depth of field so you can input the result into stackshot. You can use a DOF calculator to help you with this aspect. Once you have that figured out, you tell it how many millimeters, give it a start and end point, and it will take your shots for you.
Putting it All Together
There are a few ways to put together a focus stack. The main software is Helicon Focus, Zerene Stacker, and Adobe Photoshop.
The one I will focus on is Adobe Photoshop.
Once you have acquired all of your focus slices, you’ll need to import them into one document. The easiest way to do this is to go to File > Scripts > Load files into stack. Find the folder with your slices and select them all. Hit ‘OK’ and it will load them all as a layered document.
Select all the layers in your document and go to Edit > Auto Align Layers. For projection choose “Auto.” If you feel your image needs Vignette removal or has distortion that needs correcting, you can check the lens correction boxes, but be warned this will take significantly longer to process.
Once your files are aligned, it is now time to combine them into a stack. Go to Edit > Auto Blend Layers. Choose “Stack Images” and check “Seamless Tones and Colors.”
Once that processes, you’ll have one newly focus stacked image!
This intro is just the tip of the iceberg. Focus stacking can be a tedious process that requires many tries and lots of practice. But the end result creates macro images that appear to be taken on other worlds. The surprising detail hidden in small objects is waiting for you to discover and each time you have a successful stack, the feeling of photographically triumph is profound. I hope I have encouraged you to give this process a try. Happy stacking!