When your camera’s perception of where a lens is sharp, is a tad off.

This article was co-written with my good friend Claus Møller, with whom I have spent countless hours diving and taking photographs.

Not all lenses are created equal

Even two copies of the same lens can behave slightly differently. Autofocus systems can also be affected by small tolerances in the camera body and lens. The result may be a consistent front-focus or back-focus error: the camera confirms focus, but the sharpest point in the photograph is slightly in front of or behind the intended subject.

Many higher-end DSLR and SLT cameras provide an autofocus micro-adjustment feature to compensate for this. It can be particularly useful with fast lenses, where the shallow depth of field at wide apertures makes small focus errors easier to see.

It is worth testing your equipment before assuming that it needs adjustment. A poorly controlled test can lead you to introduce an error rather than correct one.

Can micro-adjustment damage your equipment?

No physical damage is caused by changing the micro-adjustment value. The risk is simply that an incorrect setting can make autofocus less accurate. You can reset the value and return to the original behaviour.

Be aware that some zoom lenses may not focus consistently across their entire focal-length range. An adjustment that improves focus at one end may make it worse at the other. Test at the focal lengths and distances you use most often, and decide whether a compromise is appropriate.

How do I know whether adjustment is needed?

If autofocus repeatedly places the sharpest point in front of or behind the area you selected, it may be worth investigating. On my Sony Alpha A99V, the process was straightforward enough that I tested all my lenses. Eight of the nine I tried appeared to benefit from some adjustment. The A99V can store adjustment values for up to 30 lenses.

In the example below, the red arrow marks the point selected by the camera, while the green arrow indicates where the lens has actually focused. The aim is to bring these two points together.

What you need

1. A laptop or monitor displaying the focus calibration pattern.
2. A sturdy tripod.
3. Your Sony Alpha A99V set to Spot Focus (see the handbook, page 95).
4. Set the focus peaking colour to red (see the handbook, page 102).
5. Locate the AF Micro Adjust menu (see the handbook, page 101).

Setting up the test

Set up the camera and target carefully. The target should be flat and evenly lit, and the camera should be aligned consistently with the test pattern. The original method described here uses a monitor and an angled focus scale. Monitor sharpness, pixel structure and alignment can influence the result, so treat this as a practical home test rather than a laboratory calibration.

Procedure

1. Display the focus calibration pattern on your monitor.
2. Mount the camera securely on the tripod and position it according to the test pattern instructions.
3. Use a wide aperture so that any focus error is easier to identify.
4. Set the camera to single-shot autofocus and focus on the designated focus line.
5. Switch to manual focus without changing the focus position.
6. Magnify the relevant area of the image and inspect where the sharpest point falls in relation to the focus line.
7. Make a small adjustment, repeat the test and check that the result is consistent. Do not rely on a single frame.

If the sharpest point is consistently in front of or behind the intended line, adjust the value accordingly. Make small changes and repeat the test until the focus is as accurate as you can reliably achieve.

Note: This article describes a procedure for the Sony Alpha A99V. Menu names and autofocus calibration features differ between camera models, and many mirrorless cameras use different focusing systems.