In this article, we’ll cover everything you need to know about calibrating lenses, as well as tips and tricks on how to do so at home.
Related Guide: Camera Lens Filters Explained
Why Do Calibration Issues Occur?
Front focusing is when your lens focuses on a section of the scene in front of your target subject.
Back-focusing is when the lens is focusing behind the target object.
Just because your lens is back or front focusing does not mean something is wrong with it – it could be a compatibility issue. Your camera and lens are manufactured at two different manufacturing establishments; ideally, they’re calibrated to work with each other. The particular lens and camera do not come to meet each other until you mount the lens onto the camera body. At that point, any differences in calibration show up. In most cases, that difference is only marginal, but to the trained eye, that difference is noticeable.
This calibration incompatibility is what we will be trying to correct today.
What You Need to Calibrate Your Lens
To calibrate your lens, you need the following:
- a white piece of paper
- a ruler, a pen
- a low table or a flat surface to
- a camera
- a lens (the lens you plan to calibrate)
- a tripod.
Optionally you could also have a cable release that will ensure that you don’t have to touch your camera during exposure, as this process is sensitive.
How to Identify the Calibration Error
Step 1: Place the white sheet of paper on a flat surface or low table.
Step 2: Place the ruler on the white sheet of paper and draw a line. Once the line is drawn, make sure that you move the ruler away. Removing the ruler ensures that the lens does not accidentally focus on anything other than the mark you made on the white sheet of paper.
Step 3: Now mark a point on the line that will serve as your lens’s focal point.
Step 4: Bring your camera in and set it up on the tripod.
Step 5: Once you have set up your camera, focus on the mark on the line. Switch your camera to manual focusing to ensure that the focus can be precisely set by hand. Once you have set your focus by hand, switch your camera back to autofocus and ensure that the camera focuses on the mark you drew. Make sure you use the widest aperture your lens can shoot at and choose the center autofocusing point.
Step 6: Once the image has been captured, place the ruler back on the sheet, and place the 15cm mark right where you previously made your mark. Be careful not to shift the paper in any way. If you do so, you’ll have to restart.
Step 7: Now go ahead and take another picture. Your focus was already set on the mark you had placed on the white paper, so there is no need to refocus. Ensure that your hands don’t accidentally move the camera during exposure.
Step 8: Lastly, it’s time to assess the image. Carefully review the image to see if the number 15 on the ruler is in focus. If the 15cm point is not in focus, you have a calibration issue. That means you could find that the numbers 14 and 13 are in focus instead of the number 15. It could also be that the numbers 16 and 17 are in focus rather than the number 15. Depending on the focusing distance error, you have to adjust the focus accordingly.
Adjusting the Focus: Custom AF Calibration
On Canon systems, these are the steps that you need to take to adjust the autofocusing calibration:
- Press the Menu button and go to AF Menu.
- Select AF Microadjustment.
- Under Microadjustment, scroll down to Adjust.
- Scroll along the adjustment scale and choose the degree by which your lens is back-focusing or front-focusing. If your lens is focusing further ahead, you have to select negative compensation and vice versa.
- Selecting how much to pull or push the adjustment will take a few tries. This is a trial-and-error method.
- Once you’ve made your adjustment, press Set.
- Take another test shot and readjust if necessary.
Adjusting the Focus: Nikon AF Calibration
The above are the steps you should take if you use a Canon camera for AF fine-tuning. For Nikon cameras, the steps are very similar.
- Dive into the setup menu on your Nikon camera.
- Select AF fine-tune.
- Make sure that AF fine tune is turned on.
- Make sure that AF mode is set to AF-S.
- Choose the AF area to a single point.
- Make sure your live view is switched off because live view uses a different autofocusing mechanism.
- Take another shot to see if the calibration is corrected.
- Make the necessary adjustments by going into the default option under AF fine-tune.
- Retake the shot to confirm that the AF fine-tuning has corrected the focusing issue.
- This may take several shots and trial and error before correcting the autofocusing issue.
Some Things to Consider
Getting a calibrator or a ready-made focus adjustment tool is optional. It costs about 10 to 20 dollars and gives you a professional target to set up the shot and fine-tune the AF calibration. If you don’t want to get a calibrator, you can always make one using the DIY system I explained at the start of the discussion.
Always set up your camera on a tripod and ensure it does not move when you take the test shots. Getting a cable release is a good idea. Plus, a cable release comes in handy in several ways, so it’s a good investment. Some tutorials say you don’t need a tripod, and you can do this shooting hand-held. I’m afraid I have to disagree with that approach, as this is a careful calibration process that’s supposed to be precise.
Turn off the live view option. As mentioned above, live view uses a different autofocusing process. Any calibration changes you make with a live view will not be available for use when shooting using the optical viewfinder.
Always do this entire process indoors where there is no wind disturbance and you can control the entire process. Doing this outdoors means there are chances that wind might knock the calibrator off its axis, or temperature can cause heat diffraction that can affect the preciseness of the procedure.
If you’re doing this for a combination of a lens and teleconverter, you first have to calibrate the lens and then the lens and the teleconverter together. This is because the camera will consider the lens and the lens teleconverter combo separate entities and save the values separately.