Focus Stacking: Getting the Shots in the First Place
Shooting for focus stacking can range from easy to maddeningly frustrating depending on how many shots you need to take. The higher the magnification, the shallower the depth of field and the more shots you need to get the results you really hope for. Here are two good solutions to make your shooting easier.
Your eyes automatically adjust focus when you look at a scene but not when you look at a photograph of that scene. Whatever depth of field you capture is all there is in that photograph. Focus stacking is a technique that uses software to combine multiple shots taken at different focus distances to form a composite result with greater depth of field. The technique is often associated with macro photography where the magnification employed brings with it very shallow depth of field. But it can also be used for landscape work where you need just a bit more depth of field than seems doable in a single shot. Sometimes you might be able to pull it off by stopping the lens down far enough but the resulting long exposure times could lead to blurred images from subject movement. Sometimes no matter how far you stop the lens down it just isn't optically possible to get sharp images throughout in a single shot. If only a camera worked the way our eyes do.
To make use of focus stacking, you need to first set your camera on manual exposure to ensure that all images you shoot will be consistent. Lock all the knobs on your tripod down so nothing will move. Now focus on the nearest point you want to capture and take a shot. Then refocus a bit further away and take another. Refocus and shoot, refocus and shoot, with each frame capturing another slice of the scene in focus with everything else falling where it may. You can stop once you get a sharp image of the farthest point you want to capture. Each frame needs to overlap the depth of field of the one in front of it and behind it by enough to ensure they can be merged without any visible artifacts.
All of this tends to be more difficult when shooting macro than landscape images. Available depth of field in the realm of landscapes generally covers feet or even miles, which means you shouldn't need too many frames to cover everything you are after. Also, even though it is possible that refocusing could cause slight camera movement if you're not careful, such movement would be dwarfed by the scale of the subjects being shot.
But each of these facts that work in your favor for landscape shooting ends up working against you for macro. When working with smaller subjects, available depth of field will be correspondingly smaller. So much so that it may only be a few millimeters front to back, or even less. Traditional macro shooting technique involves aligning that shallow depth of field to best align with the most important plane of focus in your subject, stopping the lens down as far as you can, and hoping for the best. But if you can get a series of shots with progressively varied focus distances you can combine them with focus stacking. But if you have to adjust the focus manually, even a very slight movement of the camera could complicate aligning your source images.
Helicon Remote shooting a small scale model of the Honda Element
65 shots automatically taken by Helicon Remote. I used a wide open aperture to get as many shots as I could. When Remote finished, I clicked the button and Helicon Focus merged the stack.
I know of two good methods to address this problem, one that I do use, and one that I don't. It's not that either method is necessarily better; it's just that I don't really need two methods. Each has strengths and weaknesses too. It all depends on your needs.
What I use I've mentioned briefly before. If you license The Pro or Pro X64 version of Helicon Focus, it comes with a great add on program called Helicon Remote. To use it, you plug your camera into your laptop (Windows or Mac OS X) with a USB cable. The program supports pretty much all current Nikon and Canon digital cameras that support a Live View mode. Once connected, you can use the program to drive your camera. It can automate shooting both focus stacking images and exposure stacking (HDR) images. The initial release a couple of years ago was a bit rough, and HeliconSoft officially still calls the program Beta software, but in my experience it works great.
The basic workflow for Helicon Remote is quite straightforward. You use buttons in the program's interface to focus the connected camera on the nearest focus distance. When you're satisfied, click another button to tell the program to remember that distance. Then do the same thing for the furthest away point you want to include in focus. The program then automatically calculates the number of exposures necessary. All you have to do is click the "Start" button and it will proceed to take all the images, changing focus for each as it works its way from front to back of your defined range. The images will automatically be uploaded to the laptop. If you want to use Helicon Focus to process the stack, just click "Yes" when the program asks you at the end of the series of shots. If you'd prefer to use Photoshop instead or another program, just click "No." You can even turn the asking off if you want. There are plenty of other configuration options including a manual mode that will let you determine the number of shots to take.
Nothing is perfect and there are few downsides to Helicon Remote. Since it only comes with the more expensive versions of Helicon Pro, it isn't cheap. Given that I licensed Helicon Focus before there were many other good options for focus stacking, I've already bought into the system. Also, to use it, you will need to have a computer of some kind to run the program on which may entail more expense if you don't already have something that will work for your shooting needs. Computers aren't noted for being extremely durable either so shooting outdoors may entail some risk. At home, I use the laptop I'm typing on right now, but I also have a smaller netbook with a solid state drive (SSD) that I have used in the field. Canon shooters should be aware that Nikon provides finer control over the distance between focus steps. I can't speak to how much of an issue this may be since I use Nikon.
The other good option I know of is using an external motorized focusing rail. Rather than changing the focus, this method moves the entire camera and lens forward and back just as one would with a manual focus rail. The most well known such solution is the StackShot from Cognisys. The system consists of the motorized focus rail together with a small control module with an LCD display. You mount your camera to the focus rail and connect it to the control module with a shutter cable (sold separately). The controller operates on 12 volts DC either by means of an AC adapter or optional battery. StackShot also has a USB interface for connection to and control from a computer. Both Helicon Focus (via Helicon Remote) and Zerene Stacker can control StackShot via USB. If you don't want to buy either program you can still operate StackShot using the standard control module. Using the StackShot seems similar to using Helicon Remote except that you control the process using buttons on the control module rather than a Windows or Mac OS program. Pretty much everything is configurable.
Just as with Helicon, StackShot has its pros and cons. As you might be guessing, it isn't cheap (I think the only method of shooting images for focus stacking that is cheap is to stick with manually changing the lens focus). There are multiple configurations available, but the starting price is over $500. Adjustment via the focus rail though can be more accurate than direct focus using Helicon Remote. Essentially, Helicon Remote is simply counting revolutions of the lens barrel with is not strictly linear from one end of the focus range to the other. On the other hand, movement of the focus rail is both precise and predictable. And since it doesn't rely on Live View support, StackShot can be used with camera models that won't work with Helicon Remote. For extremely high magnification, StackShot seems quite attractive.
Whether you can justify Helicon Remote or StackShot depends on what your needs are. You can always focus each frame manually. The more macro focus stacking work you do though, the more you are likely to be tempted by one or the other.