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Calibrate Your Lens (And AF Settings For 6D Mark II With Sigma 120-300 2.8)

Thomas’s Langur (Presbytis thomasi) eating a huge jackfruit in the jungle of Bukit Lawang, Sumatra.

Thomas’s Langur (Presbytis thomasi) eating a huge jackfruit in the jungle of Bukit Lawang, Sumatra.

As a professional wildlife photographer, you always want to have tack-sharp shots for your portfolio or clients. Sometimes the images look sharp on the back of your camera when you’re in the field, but then you get home and notice the focus is actually on that branch just behind or ahead of your subject’s eye. This can ruin a photo, making us smack ourselves and call ourselves names.

I once went to Shenandoah National Park in Virginia and spent over an hour in the middle of a small herd of deer - mostly does and young bucks. They came so close to me that some of my photos using a 300mm lens were full-frame portraits. It was amazing and I could not wait to get the photos home and onto the computer so I could share them with the world.

Unfortunately, when I got home I was incredibly disappointed with what I saw on the computer monitor. Most of the images had missed focus, focusing instead on a tree or branch about six inches to a foot behind the deer. I was heartbroken.

After researching the problem, I discovered the AF Microadjustment setting (on Canon; AF Fine Tune on Nikon). With this setting one can adjust where the focus hits, either closer to or further from the camera than is the lens’ standard setting.

I bought a focus calibration tool on Amazon and got to work as soon as it arrived. The process is easiest to do tethered to a laptop so you don’t have to keep switching the SD card from the camera to your computer, but you can also do it from the LCD screen on your camera.

Once you have your focus tool, set it up and put your camera on a tripod. Set the camera so that it is perfectly level - not tilting to either side and pointing perfectly straight rather than tilted up or down. Put the AF point in the center of the frame and point it at the center of the focus tool. Set your camera to shoot JPG since we are looking for speed over image quality.

Now take several pictures - one at -15, -7, 0, +7, +15. Check these five photos to see which has the best focus, that is sharp on the “0” but fading out evenly to the other numbers. When you find the one that is closest to correct, take five more photos in that area. For example, if the -7 photo was closest, take five more photos at -5, -6, -7, -8, -9. Repeat this process until you think the focus is set perfectly.

This may take an hour or so, but it is well worth it. This is especially true if you have third-party lenses like Tamron or Sigma, which tend to be further “off”. Now you will be taking sharp photos every time (as long as your shutter speed is high enough).

If you have the same camera and lens as I - a Canon 6D Mark II with a Sigma 120-300mm f/2.8 Sports - you are in luck. I have already done the work for you! You can just set the settings to +10 on the Wide (120mm) end and +14 on the Telephoto (300mm) side. If you also have the Sigma 2x teleconverter with this lens/camera combination, set it with the TC to +10 on the Wide (240mm) end and +15 on the Telephoto (600mm) side.

I hope you found this article helpful. Let me know if you have any questions, I know it can be quite confusing. I think I played with this for around four hours the first time I ever did it.