By Ellis Vener
It’s no secret that working professionals need to make sure that the tools of the craft work together smoothly and reliably. It is also true that just because high quality cameras and high quality lenses cost a lot, it doesn’t mean they will work together perfectly straight out of the box. Cinematographers and camerafolk in the broadcast industry, and some still photographers, have known this for decades.
While most of us still photographers are not able to cherry pick our lenses—trying several examples of the same lens to find the best one— and fewer go to the expense and trouble of having the optics in their lenses centered and collimated. Even if you do that does not ensure that the lens will then perfectly match an individual camera body. What is needed is a system for fine-tuning the autofocus system for individual lenses to eliminate the computational errors that result in front focusing or back focusing. Fortunately nearly all mid-range and high-end cameras introduced since 2007 have this. All that is needed is a method for testing and a target.
Outside of making one yourself, there are a couple of kits available to make the AF fine-tuning process easy, but the most venerable is the LensAlign from Michael Tapes Design. The original LensAlign PRO (ppmag.com review) and LensAlign Lite have now been replaced by the LensAlign MkII and MkII Plus. The difference between the standard MkII and the MkII Plus models is the size of the focusing target and the length of the ruler, with the larger target and longer ruler of the Plus model designed for use with 300mm and longer telephoto lenses. The long ruler and target of the Plus can be purchased separately and used with the basic MkII.
Both the LensAlign PRO and MkII targets consist of a target for your TTL AF system to use, a sighting method through the center of the target to make sure that target is parallel to and centered in your image sensor, and a ruler mounted at a slant. The markings on the ruler guide you in determining whether you need apply positive or negative autofocus adjustment. The numbers do not translate to the precise amount of correction but serve as a general guide and for evaluating the results using Photoshop’s emboss effect as proof of the adjustment. Both the older and current models have a standard tripod screw socket for mounting the rig on a tripod head. But there are differences.
For starters, where the LensAlign PRO came preassembled, the MkII comes disassembled and can be broken down flat to travel. Snapping the MkII pieces together takes a couple of minutes and is an uncomplicated process. Also where the LensAlign PRO allowed you to change the ruler angle, on the MkII the angle is fixed at 45 degrees.
So how does it work? Ideally, start by mounting both the LensAlign MkII and a camera on separate tripods. While you can mount the LensAlign on a light stand, it helps to use a tripod with a head so you can fine tune the height, pitch, and yaw angles. In the worse case, you only need a tripod for your camera and a surface to rest the LensAlign on.
Line up the center of the focus target with the center of your lens so that you can see all of the red circle on the back plane of the target inside the hole in the center of the target (above). The alignment process goes faster if you have an assistant moving the target while you look at the camera’s preview screen. Alignment is critical to make sure the zero mark on the ruler is not at an angle to the sensor plane on the focus target.
Once set up, shoot at different AF micro-adjust settings and the with lens wide open. Use a low ISO as well. While Canon and Nikon both recommend a target-to-camera distance of 50X the focal length, I’ve found that a 25X distance for most lenses works best. If you regularly shoot with the camera at a fixed distance to a subject, for studio headshot portraits for instance, use the target at that distance.
On most cameras the auto-focus micro adjustment range goes from -20 to +20. To speed the process along I shoot these initial series in increments of three starting at -18 (-18, -15, -12 … +18) and then import them into either Photoshop or Lightroom and view at 100%. Once I have found the best setting then shoot a second set of images at single step increments around the best result. For example, if +9 yields the best initial result shoot at +7, +8, +9, + 10 and +11.
To confirm the results, Michael Tapes suggests opening the select image in Photoshop and applying the Emboss filter. You want to look for offsets of color around the zero mark on the ruler. Once you’re confident of your results, make sure the best setting is programmed into the camera for that lens and you can move on to the next lens.
Zoom lenses present a slightly different challenge, as the settings that work at one end may not be optimal for the other. Canon addresses this in the EOS 5D Mark III and EOS 1D X by allowing for settings at both the Wide and Tele ends. We hope Nikon follows their lead.
There is one more significant difference between the older LensAlign PRO and the LensAlign Mk II: the cost. While the price of the LensAlign Pro was $179.00 while, the MkII sells for $79.95.
Fine-tuning autofocus performance really makes a difference in image quality. While it can’t turn a bad lens into a good lens, or a good lens into a great one, it will markedly and sometimes startlingly improve the results you get from that lens and camera.
LensAlign MkII: $79.95
LensAlign MkII Plus: $159.95
LensAlign MkII Long Ruler Kit (turns the basic MkII into a MkII Plus): $84.95