Here’s a (semi) fun way to start the year off right – it’s time to calibrate the focus of your lenses!
Most DSLRs offer options for “micro adjustment” or to “fine tune” the focus of attached lenses. If you happen to use Sigma ART series lenses, you can also use Sigma’s USB Dock for even more refined lens focus calibrations.
Why You Should Calibrate The Focus on Your Lenses
All lenses have some tolerance built into the manufacturing process, so not every lens focuses exactly the same.
With modern high megapixel cameras even a slight front or back focus can be the difference between a usable image and a reject.
Now, if you’re a landscape photographer who photographs everything at f/16, you’re probably not going to notice it your lens’ focus is slightly off.
However, if for example you are a portrait photographer who has invested in a set of prime lenses and you almost always photograph your subjects between f/1.4 and f/2.8 – you definitely want to make sure that your lens’ focus is bang on – because at f/1.4 the difference between your subject’s eye being in focus versus their eyelashes is a big problem.
Having said that, the only lens I have ever owned that has had a major focus calibration issue was a Nikon 50mm f/1.4. Every other lens has been reasonably calibrated.
But as I am now using a set of Sigma ART lenses for the majority of my work, and especially with the new Sigma ART 85mm, I am using f/1.4 more than ever before and with that narrow of a depth of field, I am noticing subtle focus errors more and more often.
Step 1: download your own DIY lens focus calibration target
You can download a PDF lens focus calibration target here.
This target was originally created by Toronto fitness photographer David Liang.
Assembly is pretty self explanatory, you basically stick the target to a piece of foam core using a glue stick or two sided tape, cut it out and match the tabs (I used a glue gun to secure the pieces) and then insert pins or straightened paperclips as the specified locations to hold the ruler in place.
If you want to get fancy, you could also glue a spare quick release to the bottom to make for speedy mounting on a tripod, and add a small bubble level to the top.
(David also wrote a more detailed explanation on how to assemble the target here.)
One important point – the scale of the ruler doesn’t really matter since the goal is to simply adjust our lenses as required to focus exactly at the target focus plane. But the location where the ruler bisects the target focus plane does matter: depending on where you stick the pins in the foamcore, zero on the ruler may or may not exactly line up with the target focus plane. If zero on the ruler and the target focus plane do not exactly line up, simply use the line on the ruler that does exactly line up – or make a new mark on the ruler with a fine pen.
If you’d prefer a commercially available option, you can purchase a Datacolor SpyderLensCal Autofocus Calibration Aid ($64 from B&H).
Step 2: calibrate your lenses – for non-sigma ART lenses
Here is a great video from B&H that explains the procedure for calibrating your lenses using the Datacolor SpyderLensCal Autofocus Calibration Aid, and you can use the exact same process using your DIY lens focus calibration target.
A few key points to remember:
- The camera should not be closer than 50 times the focal length, except for with telephoto lenses longer than 200mm where you should set the camera 25 times the focal length away from the target.
- This type of lens focus calibration is really only practical for prime lenses.
After that the basic procedure is just to take test photos and adjust the focus as required.
Step 2: calibrate your lenses – for sigma ART lenses
Here is a video from Sigma that explains how to use the Sigma USB Dock and Optimization Pro software to calibrate the focus of your Sigma lenses.
And here is another tutorial video that takes you through the entire lens focus calibration procedure for a Sigma lens, using a lens calibration target.
Here is Stocksy United photographer Luca Pierro’s process for calibrating the focus of his Sigma lenses (but the process could easily be adapted to all brands as well):
- Camera on tripod
- I set the camera at 1.4/160 ISO 100.
- I pointed a light directly on the focus target (so I didn’t use the MLU function)2. Focus
I pointed the center focus point to the center of the target, perfectly perpendicular to the sensor.
(I also used a tape measure to measure the different distances because you have 4 different distances to set. To measure in the right way, look for the focal plane mark symbol on the camera and start measuring from that point.)
In order to do the adjustments, you need to follow these steps:
- Take a shot setting the camera as described at point 1
- Remove the SD card and open the image in Camera Raw, Bridge, LR or wherever you can zoom in (or shoot tethered).
- Check the image at 200% to see if the focus on the ruler of the focus target is on the 0. Because it is at 200% don’t use the definition as a measurement. Instead use the chromatic aberration. So, if the 0 is green, the 3 is purple and the 1 or the number 2 is black, this means that you have some front focusing.
- Remove the lens without touching the tripod and attach the lens to the USB dock.
- Open the SIGMA software and add a + 1 or a +2.
- Re-attach the lens to the camera, insert back the SD and take a second shot.
It looks complicated but actually it is a pretty straight forward process.
Results are astonishing. I have two new lenses now!
And a few notes about setting in camera adjustments:
I set the “on camera” adjustments at zero. The Nikon focus adjustments tool is nice but you can set only ONE adjustment per lens. With the Sigma USB dock you can set 4 different adjustments (at different distances). The Sigma USB dock is another world because the lens performs totally different as the distance with the subject change.
Calibrate The Focus Of Your Lenses!
Have you calibrated the focus of your lenses? Did you find a big difference in image quality? It it worth the effort?
Leave a comment below and let us know!