Home Theory Autofocus macro lens

Autofocus macro lens

by Güray Dere

Almost all modern lenses offer auto focus. We can press the shutter release button and enjoy it without worrying about sharpness. Sports and bird photographers will highlight the importance of auto focus. The faster we focus, the less chance we’ll miss the scene. It is even more difficult to capture sharpness in tele lenses and autofocus becomes a need.

If you are using manual lens and have astigmatism (like me), your job is difficult. Because you cannot see clearly looking through the viewfinder, and you may sometimes have to choose the focus by just looking at the distance scale on the lens’s focus ring.

So how is the situation in the macro?

Autofocus macro lens can still help below 1:1 magnification and in single-frame shots. But if we want to use 1X or higher magnifications or focus stacking, things change.

Let’s go through a case. Let’s have a real macro lens and choose our magnification ratio 1X. We’re taking a photo of an insect.

First, we need to turn off auto focus if we want to keep the 1:1 magnification constant. As the lens moves back and forth for focus adjustment, the magnification ratio changes. We may not care about keeping the 1:1 magnification fixed, but we still need to know the situation.

However, there are situations that will make us suffer as we increase the magnification. These can be listed as depth of field, vibration and lack of light. Let’s look at the effects of these on a lens in autofocus:

Depth of field (DOF)

AF: As the magnification increases in macro shooting, the DOF, ie, sharpness, narrows and remains almost at a paper thickness. If we use the macro lens in auto focus mode, it is up to the camera to decide where to focus. It is very difficult for you to decide whether the focus will be on the right antenna or on the left hind leg. O the focus can be at the background. Then you can’t see the insect even if it is right in front of your lens, you just take a blank image and continue looking for the bug. When something moves somewhere during the shooting, the machine constantly changes the decision and focuses towards movement. If you have grass, leaves around, you can focus on them instead of insects. To avoid this, you can, for example, fix the center AF focal point. So you can always focus on the center, but it is not compatible with the frame you want.

Manual: You choose where you want to focus. The focus does not change as long as the camera does not move.

Score: Manual: 1 – Automatic: 0


AF: If we shoot handheld, in addition to the handshake, the heartbeat and breathing movement result in large vibrations. We need to think about the vibration here in 3D. The camera doesn’t just move up-down or left-right. It also moves back and forth. In a magnification of 4x, it has such a big impact that when you press the shutter button to take a photo of an insect’s eye, you may have a foot or get a completely out of focus image. There is no point in trying to autofocus. Because it is not possible. As the camera constantly moves, it just keeps hunting for focus. If you remember that the focus speed of the macro lenses are quite slow, they cannot reach the speed of the vibration even at 1X magnification.

Manual: The vibration problem is the same in manual shooting. A manual lens gives you an indirect advantage. You’ll save on the battery that an auto lens will consume constantly hunting for focus.

If the machine is set on a tripod, this time vibration is no problem. For the reasons mentioned above, we prefer manual focus again.

Score: Manual: 2 – Automatic: 0

Insufficient Light

AF: As we increase the magnification, we get less light on the sensor. This is a dark photograph and a dark viewfinder. Sometimes it can get worse to the levels we can’t see anything. The light must be sufficient for the auto focus system to function properly. Most auto lenses cannot focus properly in dim lighting conditions. As the magnification increase, the light will decrease, and the autofocus system will not be able to detect the bug, but will continue to move forward and backward and seek focus.

light and magnification
Light falling on the sensor at different magnification values

Manual: Due to the darkening of the viewfinder, we have difficulty in manual focusing. It doesn’t matter whether it’s hand-held or fixed, a dark viewfinder is a problem.

In this case, we seek assistance from a continuous light source such as a flashlight. Whether it’s manual or automatic, it will make things easier and we’ll be able to see the insect we want to shoot. So I give equal points to automatic and manual focus.

Update: I gave up the idea of equal points. Since we always do focus stacking in macro shooting, the first frame of the shot does not have to be sharp. What is important is to perform a full front-to-back scan. If we need to shoot 30 frames and we can’t see the viewfinder clearly,  we can start the shot a little further ahead and shoot 35 frames instead of 30, so we don’t need so much light. That’s why I vote for manual again. If we had used AF, we would never have been able to shoot.

Score: Manual: 3 – Automatic: 0

As you can see, we prefer manual focus in macro photography. We fix our equipment at a certain magnification. We focus on where we want by moving the camera forward or backward. The back-and-forth moving camera sounds weird, but once you try it you can understand why it should be like that.

Some manufacturers put a button on autofocus macro lenses to limit the working distance.  We can set the lens to work only at close focus or only at distant focus. This way, the lens moves faster in a shorter range, rather than going from closest focus up to the infinity while searching for focus. A handy feature for those who insist on autofocus to lose less battery and less time 🙂

Equipment used in high-magnifications are not just manual, they don’t even have the possibility to change the focus in any way. The focus distance of the lens is fixed. We change it with devices such as bellows and tubes and adjust the appropriate magnification. In such applications, auto focus is not even mentioned.

Canon’s famous MP-E 65mm works in the 1X-5X range and is designed to work only with manual focus, although it is one of the most modern macro lenses.

Of course, we have the opportunity to use manual focus on other modern macro lenses. I keep the autofocus feature off continuously when I shoot macro with my Tamron. I only turn on AF when shooting portraits.

All of the older macro lenses come with manual focus. You do not need to consider this as a disadvantage and spend 5 times more. There is even a possibility that some older lenses may be sharper. I personally ignore the criteria for being automatic or manual focus when looking at the lens properties.

Advantages of manual focus in macro shooting

  • Fixed magnification. If the focus does not change, the magnification remains constant. Our perspective problem is reduced in focus stacking.
  • We will focus exactly where we want it. We’re in control.
  • We save battery.
  • Manual lenses are cheaper.

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