Autofocus macro lens
Almost all modern lenses offer autofocus. We press the shutter without worrying about focus and enjoy it. In dim environments and wide-aperture portrait shots, autofocus comes to the rescue. Friends who shoot sports and birds will stress the importance of autofocus even more. The faster we focus, the less likely we are to miss the scene. Since it’s even harder to nail focus with telephoto lenses, autofocus appears as a necessity.
If we’re using a manual lens, we may need more shots to nail focus. Hitting moving targets—like small children—is extra hard. And if, on top of that, you have a vision issue like astigmatism that you can’t correct with a diopter adjustment (like me), focusing can turn into torture. Since you can’t see sharply through the viewfinder, sometimes you may have to eyeball focus just by looking at the distance scale on the lens’s focus ring.
Fortunately, mirrorless cameras largely solve this. Let’s still examine the situation from a macro perspective.
So how about in macro?
At the close-up level—that is, below 1:1 magnification—and for single-frame shots, an autofocus macro lens can still help. You press and shoot. Job done. But what if we’re working at 1× and above, or we’re going to do focus stacking?
Let’s go with a scenario. We have a true macro lens in hand. Let’s set our magnification to 1×. Let’s say we’re photographing an insect.
First of all, if we definitely want to keep 1:1 magnification constant, we need to turn off autofocus. Because in most macro lenses, when focusing, the movement of the optical elements inside the lens causes small changes in the magnification ratio. This is also called “focus breathing,” and it can create perspective differences, especially in precise work like focus stacking. If we’re not obsessed with 1:1, we don’t care—but we should still be aware of it.
As we increase magnification further, a set of challenges grows with it. These can be listed as depth of field, shake, and insufficient light. Let’s examine how these play out with an autofocus lens:
Depth of Field (DOF)
Automatic: As magnification increases in macro, DOF—i.e., the in-focus zone—shrinks dramatically and can be as thin as a strand of hair. If we use a macro lens in autofocus mode, where focus will lock is left to the camera’s decision. It’s very hard for you to decide whether the insect’s right antenna or left hind leg will be sharp. The focus may keep hunting and drift far back, wandering somewhere deep. Even if the insect is right in front of your lens, you may not see it. You just get an empty blurry image and keep searching for the bug. You may not even be able to tell if the lens is pointed exactly at the insect. As things move during the shot, a bit of wind stirs leaves, etc., the camera keeps changing its mind, reacts to movement, and may focus on different points. Whatever enters the frame—grass, twigs, etc.—you might end up focusing on those instead of the insect. To avoid this, you can lock the AF focus points, for example fixing the center point. That way you always focus on the dead center, but that often won’t match the framing you want.
Manual: You choose exactly where you want to focus. As long as the camera doesn’t move, focus won’t change.
Score – Manual: 1 Automatic: 0
Shake
Automatic: If we’re shooting handheld, in addition to muscle tremor, heartbeat and breathing cause wide-swing vibrations. We need to think of this vibration in 3D. In our hand the camera doesn’t just move up–down or left–right. It also moves forward–back. At a magnification like 4×, it gets to the point where, when you press the shutter to shoot the insect’s eye, it may pull its leg back—or you may get a completely empty blur. There’s no point trying to autofocus a macro lens here. It’s simply not possible. Because the camera is constantly moving in our hand, the camera constantly hunts focus. If you recall that macro lenses have slow focusing speeds, even at 1×, autofocus speed can’t keep up with the speed of the shake.
Manual: The shake problem is still there for handheld :) Nothing becomes easier when you use a manual lens. But a manual lens gives you an indirect advantage regarding shake: you save the battery a constantly hunting AF lens would have consumed.
If we fix the camera on a tripod, then shake stops being a problem. Autofocus or manual—both offer the same comfort for focusing. Because of battery consumption, I still prefer manual focus.
Score – Manual: 2 Automatic: 0
Insufficient Light
Automatic: As we increase magnification, less light reaches the sensor. This shows up as insufficient light in the photo and a darkening viewfinder. Sometimes it can get so bad that we see nothing. For an autofocus macro lens’s focusing system to work properly, the light must be sufficient. Most AF lenses can’t focus well in dim conditions. In macro shooting, as magnification increases, light will decrease; due to this darkening, the AF system won’t be able to find the insect and will keep moving back and forth hunting for focus.
In this case we get support from a continuous light source like a flashlight. Whether manual or automatic, thanks to the flashlight things will get easier, and we’ll be able to see the insect we want to shoot. For this point, giving equal scores to automatic and manual focus could work.
But thinking a bit more, I gave up on equal scoring. In this type of macro shooting, we almost always do focus stacking, so it’s not essential that the first frame be focused on the exact frontmost edge of the subject. What matters is performing a complete sweep from front to back. So if we’re going to shoot 30 frames, and because we can’t see the viewfinder clearly we start a bit further forward and shoot 35 instead of 30, the lack of light no longer matters. That’s why I’m casting my weighted vote for manual again: manual gets 1 point, AF gets 0.5. Without a flashlight, if we had used AF we wouldn’t have been able to shoot at all; with manual, we could complete it without missing anything.
Score – Manual: 3 Automatic: 0.5
As you can see, in macro photography we prefer manual focus. Whatever magnification the framing requires, we first set our equipment to that magnification—or in other words, that focusing distance. Instead of fiddling with the lens to change the focus area on the insect, we move the entire camera—handheld or fixed on a tripod—forward and back to focus where we want. A body moving back and forth sounds odd, but once you try it you’ll understand that’s how it should be.
Some manufacturers put a switch on autofocus macro lenses to limit the working distance. For example, on the Tamron 90mm f/2.8 1:1 macro, when we flip this LIMIT switch, the lens restricts itself to work only at close range or only at long range. Instead of hunting focus all the way to infinity and then coming back to macro range, it does it within a shorter span and goes back and forth faster. A handy feature for those who still insist on autofocus so they waste less battery and less time :)
With equipment used at high magnifications, not only is autofocus impossible, but there’s often no way to change focus at all. The lens’s focusing distance is fixed; we adjust the appropriate magnification by changing it with devices like bellows and tubes. In such applications, autofocus isn’t even mentioned.
Canon’s famous MP-E 65mm model works in the 1×–5× range, and even though it’s one of the most modern macro lenses, due to the situations mentioned above it is designed to work with manual focus only.
Of course, on most modern AF macro lenses we have the option to use manual focus when we want. When I’m doing macro with my Tamron, I keep the autofocus feature off all the time. I only turn AF on for portraits.
All the slightly older macro lenses present themselves with manual focusing. You don’t need to treat this as a disadvantage and spend 5× more chasing the latest tech. In fact, some old lenses may even be sharper. When researching lens specs, I personally completely ignore whether it’s automatic or manual focus.
To wrap up:
Advantages of using manual focus in macro
- Fixed magnification. If focus doesn’t change, magnification stays constant. Perspective issues decrease in focus stacking work. - We focus exactly where we want. Control stays with us. - We save battery. - Manual lenses are cheaper.
