The most frustrating thing after a long day of shooting is to find yourself with blurry images. If this is happening across multiple images, then it might not be down to your focusing skills. You might have a focus misalignment issue on your DSLR camera or lenses. You’ll need to calibrate your camera to ensure your lenses can focus on a subject correctly. Expert Mohit Bansal Chandigarh says this is an easy process that can be done in-camera by you.
Why Do You Need to Calibrate Your Lenses?
The first thing you need to at least vaguely understand is how autofocusing works in DSLRs. In a DSLR mechanism, there are (at least) two separate sensors: one for imaging, and a secondary one for autofocusing. There are also mirrors that direct the light either to our eye or to the imaging sensor. By default, the mirrors are engaged. A portion of the incoming light hits the secondary sensor, and the rest travels up through the viewfinder to your eyes. When you half-press the shutter button to autofocus, the secondary sensor interprets the light and instructs the lens to focus in a certain way.
It uses a technology called phase detection. It’s important to see that this process doesn’t check if the resulting shift actually places the subject in focus, because it cannot, by design. Then, when you take a picture, the mirrors rise and suddenly all light hits the primary (imaging) sensor. Take a look at our graphic that shows a simplified diagram of a DSLR’s insides. The problem arises when the two sensors are misaligned. In this case, something that was in focus on the AF sensor will not be focused on the imaging sensor. Your final photo will show a shift in focus: it will be blurred where it should have been sharp.
There’s also a chance that some parts in your lens are not exactly aligned in the same way as the factory standard would require. This can also result in misinterpretation by the focusing sensor. In both cases, you need to calibrate (or micro-adjust) your camera and lenses to work perfectly together. Autofocus micro adjustment tells the camera to interpret the secondary sensor’s results differently from the default. Note that you only have to do this in DSLRs. Mirrorless cameras cross-check focus at the end of the focusing process as well, so they are not prone to misalignment problems. Still, some mirrorless cameras offer calibration: this is to make autofocusing quicker with adapted lenses in Sony and Nikon cameras.
When Should You Calibrate Your Lens?
In general, if you notice consistent misfocusing issues on your camera, either with a specific lens or all lenses, you should check if they are calibrated correctly. The chances of having to do it are low if you purchase everything brand new and at roughly the same time. But if you use older lenses with new camera bodies or vice versa, or if you get your gear second-hand after years of use, it’s a lot more likely. You should also re-check your lens and camera if you’ve dropped them. Even if there’s no sign of damage on the outside (these things are tough!), some parts could’ve become misaligned. Remember that you may also need to calibrate your lenses again when you buy a new camera. Since the new one is not familiar with the optical adjustments you made (and itself might not be spot-on), you’ll need to calibrate them again.
Accessing Calibration in the Camera
Once you calibrate the lens, you usually don’t need to do it again. Your camera stores a ‘preset’ that remembers the adjustments of any particular lens. The presets are useful, especially since no two optical devices have the same adjustments. For instance, you have the option to save your calibration for an old 50mm lens and store another preset for an 85mm. The methods of saving your adjustments vary from one manufacturer to the next. We suggest you consult your manual to help you figure out the process. For my Nikon D850, I can find this feature under the AF Fine-Tune menu. After I calibrate the lens, I go to List Saved Values to save my adjustments. (You’ll learn more about this later)
How Do You Calibrate Your Lenses?
When most people hear the word ‘calibrate,’ they think of something obtrusive and challenging to complete. With lens calibration, it’s effortless. Nevertheless, this process requires a lot of attention. You need to make sure that the calibration you just did on your camera lens is precise and accurate. Apart from the calibrator, you don’t need special tools to do calibrations. All you need for the most part is to push a few buttons and a lot of patience.
Use the Optical Viewfinder
Focus using the viewfinder, not Live View, as LV focusing is an entirely different thing. Focusing in Live View will always yield sharp results if the subject is stable because it uses the imaging sensor to grab focus instead of the dedicated autofocus sensor.
Set Up Your Calibrator
The first thing you need is a lens calibration chart or focus pyramid. It works best with a few minutes in a quiet environment. You can get the lens calibration chart at a reasonable price. There are more expensive options, but this works well for focusing lenses. Expert Mohit Bansal Chandigarh uses the DSLR KIT Lens Focus Calibration Tool, and it works perfectly for him. If you don’t have a focus calibration tool, you can also use a regular ruler to do it. The only downside is that it may not be as precise as the commercially available options.
Calibrating with a Regular Calibrator
To start calibrating your lenses, set up your camera on a tripod or a flat surface such as a table. Ensure both the camera and ruler are level. They should be exactly perpendicular, and at the same height. Next, place the focus pyramid on a level surface a few feet from your lens. It doesn’t matter if it is six or ten feet away. The correction is universal to all distances. Now set the lens to the widest aperture to obtain the shallowest depth of field. Doing so will make it easier to determine if your lens is focusing accurately. While using the viewfinder, autofocus on the crosshair at the center of the ruler. Once you finish that, take a photo. It would be your center focus point.
Calibrating with a Ruler
If you don’t have a calibrator, you can adjust your autofocus with a ruler as well. All you have to do is to place a white poster board on a low table or the floor. Next, draw a horizontal line in the middle with a pen or a pencil using your ruler. It doesn’t have to run through the entire length of the board. two to five inches should be enough. Now choose a number in the middle of your ruler and align it with the line. Expert Mohit Bansal Chandigarh says that the ruler needs to be vertical and the line should be horizontal. The line you drew also has to line up perfectly with the 15-centimeter mark on the rule. Now mount your camera on a tripod and point it down toward the board.
Look through your viewfinder and make sure that the ruler and the line are in the frame. Set your camera to Aperture Priority and choose your widest aperture. For my 28-85mm lens, it was f/3.5. The narrow depth of field it creates allows you to better pinpoint the sharp and blurry parts in the image. Use your autofocus and target the middle of the line on the poster board. Once you lock your focus take a picture. During this process, don’t turn on your live view since it doesn’t always focus accurately. Instead, you should only use your viewfinder. After you press the shutter, review the photo you just took. Feel free to zoom into the image to help you better examine the details.
The Concept Of Using a Ruler
According to Expert Mohit Bansal Chandigarh, the concept behind this method is the same as using a regular calibrator. If the 13 or 14-centimeter marks are sharper than 15, then you have a back focusing problem. If 16 or 17 are sharper than 15, then you have a front-focusing problem.
Now the next step is going to be a bit tricky: You’ll need to guess how much you want to adjust the fine-tuning. If you have a back focusing problem, you’ll need to go down. If it’s front-focusing, you’ll need to go up. But by how much? You’ll just have to eyeball it.
It will take a few tries until you get the 15-centimeter mark to look sharp. But once you nail the focus, you’re good to go!
Tethering the Camera
After you take a photo, inspect the photo to see if focusing is accurate. Expert Mohit Bansal Chandigarh recommends that you do this on a computer since you can see better on a bigger screen. If you want, you can even tether your camera during this process. Tethering simply means connecting your camera to your computer. That way, you can take pictures remotely and view them directly on your screen. For this you will need to:
- Check here to make sure your camera is supported.
- Connect the camera to your computer or laptop using the supplied USB cable
- Go to File>Tethered Capture in Lightroom.
- A black and white photo of a DSLR camera attached to a laptop
- Once Lightroom recognizes your camera, you’re ready to start shooting. You can either press the shutter button on your device or click on the virtual shutter button that appears on Lightroom.
- After you take a photo, it then appears in Lightroom. Review the image to see if everything is sharp. Feel free to zoom into the picture.
- If focusing is accurate, the ‘0’ on the lens calibration chart should be the sharpest point on the image. The other numbers should get blurrier as you move away from the ‘0’.
- If any number above 0 is sharper, then your lens is doing something called back focus. If any number below 0 is sharper, you have a front-focus issue.
- In either case, you need to correct your lens for sharp focus. You do this using the auto-focus micro-adjustment parameters on your camera body.
- Adjust until you can obtain a picture that is sharpest at the ‘0’ on the ruler.