Treat each end of the zoom range as if it is a separate prime lens, so with our 24-70mm example calibrate the 24mm end at a distance suitable for a 24mm lens and then a separate calibration of the 70mm end at a distance suitable for a 70mm lens. The target distance required for calibration of zoom lenses will vary. The procedure for cameras which support this feature is to calibrate the zoom lenses twice, once each at both extremes of the zoom range (for example calibrate at 24mm and then a second calibration at 70mm for a 24-70mm zoom). “two point adjustment” exists on a sub-set of Canon and Nikon cameras you can find which cameras support this feature in the section titled “Wide and Tele Calibration” on the Supported Cameras page. One value is applied for fully zoomed out and one for fully zoomed in, with the camera interpolating the required mid-zoom adjustment automatically.

Most Canon cameras and the newest Nikon camera(s) now have “two point adjustment”. What you will notice is a huge improvement in auto focus compared to the previously un-calibrated lens!Ĭanon and Nikon have implicitly acknowledged the need for multiple microadjustment points on zoom lenses by allowing users to calibrate at both ends of the zoom range. In real world shooting you probably won’t notice a difference between +13 or +14 so either will work. In the example above we’d suggest a calibration value of +13 or +14. Which value should we actually use given our example? Well, focus errors have a greater impact at the telephoto end of a zoom lens as the depth-of-field is more shallow, it’s therefore better to bias the calibration value toward the telephoto end result. See directly below for a more considered approach. Since in this example both calibration results are on the positive side and the lower value is +10, almost any positive calibration value would make the lens better at any focal length than it would have been at the default setting of 0. If we calibrate at 24mm with a result of +10 and at 70mm and get a result of +15.

It’s easiest to explain this with a quick example (below). Whilst Reikan FoCal cannot address the lack of support in a camera for multiple microadjustment values, you can still calibrate a zoom lens and get a better result than an un-calibrated zoom. What you tend to find is the ideal auto-focus calibration value may vary between zoomed in and zoomed out, with the most difference seen at each of the zoom extremes. Most cameras only support a single micro-adjustment setting for the whole lens at all zoom positions.

Reikan focal multifocus target