In the opening of my Mar. 21, 2014, photo shoot post, I promised a review of my experience using the LensAlign Mk II by Michael Tapes Design. This is a tool that allows you to calibrate your lens’ auto-focus capability to your camera body. I am testing Canon equipment. Other brands of cameras can also be tested in a similar fashion. Please refer to your owner’s manual for specifics.
Why might you need to calibrate your equipment? Your camera and your lens are each manufactured to fall within a certain range of tolerance for AF. Most will likely be close to the middle of that range and work fine as a combination (when the lens is on the camera). But it is possible that the camera you buy is within the range of tolerance but it is to the extreme left or right. Likewise, your lens could be within tolerance but all the way near the other extreme. When you use the lens with the camera body, AF may not be as accurate as it can be due to this mismatch. You may have good reason to believe there is a mismatch if you are consistently getting soft images. But the way to know for sure is to test your lens/camera combination, and one way to do that is to get the LensAlign Mk II target, which sells for about $80. If you can go in with another photographer or two and divide the cost up, you may be more likely to buy this item. My daughter and I went in together and bought the target then spent an afternoon at her house calibrating my Canon 500 and my two extenders to my 5DM3. There are also other websites that offer free downloads and printing of ‘home-made’ targets.
Oh, I almost forgot to mention that only certain later model cameras have the feature (lens micro-adjustment) that allows you to make AF adjustments to fix any mismatch. Check the owner’s manual or the Internet to see if your model of camera has this feature. If your camera doesn’t have this feature you would need to ship your equipment to the manufacturer to get it calibrated.
Each lens/camera combination must be tested separately. For instance, I tested my 500 by itself with my 5DM3, the 500 + 1.4x, and then the 500 + 2x with the camera. If I wanted to calibrate the lens to a second camera body, I’d have to retest all the lens combinations with that body as well. The camera remembers what level of adjustment to apply to each lens combination once the adjustment is registered in the camera.
Here’s a run through of what my daughter, Kimi, and I did in the test. Kimi got her laptop out and installed the EOS Utility which allowed tethering of my 5DM3. We connected the 5DM3 to the laptop using the appropriate USB cable. Kimi ran the laptop while I did the shooting of the target with the camera mounted to a tripod. We assembled the LensAlign target according to its directions and mounted it on a tripod.
We started with the bare 500mm lens attached to the 5DM3. We put the target and camera at the same height. I walked behind the target and looked through the parallel alignment hole which, when adjusted correctly, assures that the camera is parallel to the target. We made sure that lighting on the target was adequate for the AF to lock onto–Kimi pulled out an auxiliary studio light for this purpose. Camera to target distance is supposed to be no less than 50 times the focal length of the lens. So, for my 500mm lens, that is at least 80 feet. Now, I have to say, this distance did not work well for us. The assembled target is not much bigger than a sparrow, and I would rarely expect a decent shot of a small bird like that at 80 feet. I was more inclined to use twice the minimum focus distance (MFD) as a good distance, which is about 25 feet. The resulting image at 80 feet had to be enlarged so much to see it that individual pixels became visible, defeating the purpose of the test since we couldn’t tell if the target was in or out of focus. Since you have to be able to analyze the image and be able to tell whether it was focused or not, the 80 foot distance was not working. It’s possible a camera with a cropped sensor might work better at the longer distance, but I haven’t tried it yet on my 7D.
Here are Canon’s recommendations for how to set the camera and lens for this test:
? Mount the camera on a good tripod.
? Set up a target for the camera to focus on. The reference target should have sufficient contrast for the AF system to detect. It should be flat and parallel to the camera’s focal plane, and centered.
? Lighting should be bright / even.
? Camera-to-subject distance should be no less than 50 times the focal length of the lens. For a 50mm lens, that would be at least 2.5 meters.
? Set the lens for AF and the camera for One-Shot AF, and manually select the center focusing point.
? Shoot at the maximum aperture of the lens via manual mode or aperture-priority. Adjust exposure level to get an accurate exposure. Use low ISO setting.
? If the lens has an image stabilizer, turn it off.
? Use a remote switch or the camera’s self-timer to fire the shutter. Use mirror lock up as well.
? Take three sets of images at microadjustment settings of -5, 0 and +5, i.e, three consecutive images at -5, three consecutive images at 0, and three consecutive images at +5.
? Look at the images on your screen at 100% magnification.
? Take additional sets of test images at different microadjustment settings if necessary until the sharpest image is achieved.
? Register the corresponding microadjustment settings in the camera.
We tested the 500 bare, 500 + 1.4x, 500 + 2x, and my 24-105. For the zoom lens we tested both the 24mm end and the 105mm end and entered a setting for each into the camera. I’ve read though, where it might be good to test zoom lenses at the most used focal length instead of at each end.
We didn’t have time to test my lens combinations with my 7D back up camera. If we had, we would have had to repeat all tests with the 7D since the microadjustment amount would probably be very different for each combination with the different camera body.
On the 5DM3, the microadjustment is made in the menu on the camera in the AF section–last tab.
I’m glad I did the test and now feel I am shooting with equipment that is maximized for accurate AF. The most I had to adjust was a +7.
Whether it is worth it to spend $80 on the target is a personal choice. For Kimi and I, we didn’t want to spend any time manufacturing a target that would be tripod capable. It took long enough just doing the tests. The LensAlign Mk II is a well made target and takes only a few minutes to assemble. It does not come with very comprehensive instructions on actually performing the tests. One can Google how to use it and get many choices online. We ended up going with instructions posted by wildlife photographer Art Morris–Birds as Art. There are also targets that can be downloaded for free but I have not looked at any and have no idea how useful they are. I suppose it wouldn’t hurt to try these free ones first.
I hope this helped in some way. Let me know if you have any questions or comments.