Using a metal ruler
IF YOU don’t have the budget or feel that buying a lens calibration chart isn’t worthwhile, a humble metal ruler is the next best option for testing your lenses. Use the inches scale, and half an inch equates to one numbered section of the Spyder LensCal. This option takes a little longer than using a dedicated lens chart and can be fiddly, but the results can be just as effective.
If you’re using a metal ruler follow the tutorial but secure the ruler with a clamp attached to a light stand or tripod at a 45° angle or position it at the edge of a table using books to raise one end. Instead of focusing on the focus target, focus on a measurement in the middle of the ruler so you have a number reference. when shooting with a lens set to a wide aperture where depth-of-field is shallow, if AF is locking on around the selected focus point rather than actually on it, the desired part of the subject could be just out of focus which could, in turn, ruin the shot. While focus drift can cause serious problems, but it’s not something you have to accept.
Thankfully there’s an easy fix that can be achieved by manually calibrating your lenses in the comfort of your own home, and while it may sound a complicated and time-consuming process, it’s the complete opposite. With the right accessories and a little patience, you can check the calibration of all your lenses and make the required adjustments for better AF performance in the future.
Testing your lenses
The first step in lens calibration is checking whether they’re focusing correctly using either a calibration chart or a metal ruler. Both options work well, and we’ll cover both, but for the best and most accurate results, a calibration chart is quicker and easier to use than a ruler. A calibration chart consists of a clear focus point with a numbered scale to the side that will show the accuracy of a lens’ autofocus.
The initial lens test will tell you whether or not a lens is focusing correctly. If it is, fantastic, move onto the next, and when you come across one or more where the point of focus isn’t where it should be you can adjust the AF parameters within the camera menu, re-check focus
using the calibration chart and adjust again if necessary until focus is spot on – it’s that simple. But while this task may sound like the light at the end of the tunnel of your lens woes, it’s far from capable of fixing every lens issue you may be experiencing.
Limitations of calibration
Lens calibration is a simple task that can make great lenses outstanding, but one thing that it can’t do is work miracles – it can’t make lenses with optical deficiencies sharper. If you have a cheap lens that’s soft this can’t be remedied, but if you have a lens that’s not focusing accurately, such as front or back focusing, this is exactly what lens calibration will fi x to provide sharpness at the exact point of focus.
When you calibrate a lens through the camera body, any adjustments made to the AF will only apply to that lens when it’s attached to a specific camera body. If you have more than one camera body, you’ll need to calibrate each lens to each body you own, although if you use certain Sigma lenses you’ll be able to hook them up to the Sigma USB Dock and calibrate the lens itself so that any AF adjustments made will apply regardless of the camera body used. We’ll take a closer look at this later.
One common fear of lens calibration is that if you get it wrong, you’ll damage your lenses, but this couldn’t be further from the truth. Calibration is performed by making in-camera micro-adjustments for specific lenses that will only be ‘turned on’ when the lens is attached. If you’re unhappy with results you can reset the calibration value back to zero, so you can never go wrong. The same applies to Sigma lenses adjusted using the dock, although with this approach you need to use the dock and software to reset values.