Focusing For Macro
A lot of folks seem to be using the current situation to try their hand at macro photography. Macro presents a lot of possibilities, even without leaving home, but a lot of challenges, too. Sometimes, focusing can be a real pain.
The inherent problem with focusing when shooting close-up images is that there is so little depth of field available. Depth of field, or the range of distances that will appear acceptably sharp within an image, decreases as magnification increases. Get close enough, and your depth of field will shrink to a fraction of an inch. It seems so simple. If only you could get the darned thing in focus.
There are many ways to shoot close-ups. Dedicated macro lenses are available in a range of focal lengths and price ranges. As an alternative, extension tubes, teleconverters, diopter filters, and other solutions exist that can allow you to get closer with regular lenses. And while there is some variability based on lens design and other factors, none of these will make a dramatic difference in depth of field. Most any means chosen to achieve a given magnification will have a similar effect on how much you will see as in focus from front to back when you look through the viewfinder. Or at the resulting images.
Given that you have so little to work with, it makes sense to get the most bang for your buck from the limited range of focus you have. Examine your chosen subject. If it has a predominant plane that reveals sufficient detail, carefully align your camera back with that focus plane. Doing so will ensure that more of what you are after will fall within limits available at that magnification. If your subject is too irregular in shape to make this practical, you'll have to make some hard choices as to what to show and what parts to sacrifice, allowing them to fall into a softer focus or blur. But fear not. An image that reveals just a single sharp edge can sometimes work quite well as a minimalist statement or abstract. It isn't always easy, but such challenges can force you to dig a bit deeper and unleash a hidden reserve of creativity you didn't realize you possessed.
Regardless of how you approach your task, a tripod is all but essential. You need a stable platform to make sure your tripod remains stable. When your subject is tiny, even a small shift in camera position can have a big impact.
If you usually rely on autofocus, you're in for a surprise with macro shooting. With such a shallow depth of field, autofocus can have a difficult time locking on. The lens will hunt forward and back, attempting to detect focus. Whenever it comes close, it overshoots the mark, unable to stop in time. As you watch through the viewfinder, your subject will get sharper, and then less so. When the lens reaches the end of its range, the whole process will begin again. As the focusing helicoids work their way back in the opposite direction, they will almost surely fail to stop in time once again. You may get lucky sometimes, but relying on autofocus will often yield nothing but frustration. Most of the time, photographers want lenses that can focus fast, but close-up work isn't one of them. You will have much better control if you go old-school and switch to manual focus. In manual mode, the focus indicators in the viewfinder will still indicate how you are doing, but this way, you can slow things down enough to stop in time.
For the ultimate in control, use a macro focusing rail. Such devices consist of a camera mounting bracket atop an adjustable bar that can precisely be moved along an axis. To use one, first, point the lens at your subject and rough focus as usual. Then, let go of the lens focus and slide the macro rail forward or back as needed until you have things razor sharp.
If you find that you still can't get sufficient depth of field, it's time to consider focus stacking. By taking a series of shots varying only in focusing distance and then merging the set in software, you can built a composite image that utilizes the sharpest portions of each frame. If done with attention to detail, the result can look completely realistic, even though no camera could have possibly taken it as is. This innovative method is quite similar to how images are constructed in the human brain. As we look at an object, especially up close as in macro work, our eyes adjust focus autonomically, and generally without our conscious awareness.
To shoot for focus stacking, you will want to have a solid tripod that won't run the risk of moving between frames. Use a focusing rail if possible, and don't touch your camera any more than necessary to avoid shaking it. Software choices in today's world for merging the shots are plentiful. If you're on an Adobe Creative Cloud plan with Photoshop, that would be a great place to start. As third-party alternatives, consider Helicon Focus or Zerene Stacker.