Guide to Lens Calibration

Ever get a new lens that’s supposed to be super sharp and come back from a day of shooting disappointed?

Maybe you were focusing on the eyes and your subject’s nose or ears came out sharp.

Or maybe you wanted a central subject to be in focus and instead, some element in the foreground or background came out crystal clear.

If this happens across multiple images it may not be your focusing abilities. If you’re shooting with a DSLR and following all the rules for getting sharp images, yet your images are still coming out soft, you may need to calibrate your lens.

Even if you’re not having focus problems, it doesn’t hurt to calibrate all your lenses if your camera supports it, especially if you’re shooting with a high-resolution camera, where any mistakes in focus will be much more obvious.

Camera lenses are delicate and complex things. This article will explain what lens calibration is and a few different ways to do it properly.

What is Lens Calibration?

 

We spend a lot of money on camera gear – and expect it to work as described – but what we’re not told is that from manufacturer to manufacturer and lens copy to lens copy there are almost always slight variances.

The exact spot where light is being focused onto the sensor doesn’t always end up in the same place. These variances are what lens calibration addresses.

If you’re shooting with a modern DSLR, your camera probably has a setting – usually called AF Microfocus or AF Fine Tune – that allows you to move the focus point either closer to the camera body or farther away from it.

If your lens has its focus shifted behind the area you’re targeting (back focusing) you’ll want to shift the focus point towards the camera body.

If the area that’s sharp is in front of the spot you were targeting (front focusing) you’ll want to move the spot farther out.

On most cameras, the focus point can be adjusted in small increments, usually spanning from -20 to 0 +20. Move the point into the negative numbers (closer to the camera) to compensate for back focusing and into the positive numbers (away from the camera) for front focusing.

Once dialled in, your camera will save these settings to memory and automatically load them in when you use this lens. It’s really an awesome feature, and crucial for all DSLR users.

Note: Lens calibration doesn’t make any physical changes to your lens or camera. We’re only talk about changing settings in your camera.

Do you need to calibrate your lenses?

If you’re shooting with a DSLR and not having focus problems, you don’t particularly need to calibrate each of your lenses.

You probably won’t need to if you’re shooting with a low-megapixel camera (i.e. 12MP) either – slight focus issues don’t tend to be as noticeable then.

However, if you’re using a high megapixel camera (say 25MP or above), any error in focus is likely to be obvious.

You’ll also want to calibrate your lenses if you tend to shoot at your widest aperture or are using a particularly fast lens.

Shooting wide open already has a narrow window of error. Add your lens being a little off and you’ll likely find yourself with the focus just a bit off more often than not. (Landscape photographers and others who shoot at low apertures probably won’t notice slight focus issues much.)

Mirrorless camera users are in luck, since the majority of mirrorless cameras use an entirely different method for their focus calculations. Where DSLRs use a focusing sensor that is separate from the sensor chip, mirrorless cameras calculate their focus directly off the imaging sensor chip.

The exception to this is the Nikon Z7. It uses the Phase Detect AF Pixels focus system, which is the same autofocus system found in Nikon’s DSLRs.

Also, some mirrorless cameras will have the option to do AF Micro adjustments (i.e. the Sony A7 series)  to correct for combating lens element displacement issues or to get better results from lens adapters like the Metabones or the Sigma MC-11 adapters.

But in general, you shouldn’t have to calibrate your mirrorless camera’s autofocus system (except for the Z7).

How often should you calibrate your lens?

How often you should calibrate your lens really depends on how you use it. For heavy and/or rough use, opt for re-calibrating roughly every six months or so. For occasional or recreation use, you can push that up towards once a year.

It’s also useful to fine-tune your camera lens if you’re shooting in super hot or super cold weather, as temperature extremes can affect the calibration values.

(If you’re looking for how to calibrate your monitor, see here.)

How do you know if Lens Focus is accurate?

The easiest way to know if your lens focus is accurate is by using one of the methods detailed below for lens calibration.

Basically, if the area you told the camera to focus on is indeed the sharpest point in an image, your lens focus is probably accurate.

Still, it’s good to check – especially if you’re noticing the sharpness of your focal point being a little “off.”

(You may even find that you need to repair your camera lens.)

How to Calibrate a Lens

There are a number of different ways to calibrate your lens, ranging from free-but-complicated to pricy-but-simpler. Below you’ll find three of the more common methods.

We’ll start out with how to calibrate a lens using an inexpensive calibration tool (recommended), then the most common DIY method (OK, but not as easy or accurate), and finally lens calibration via software (pricy).

Finding Lens Calibration in your Camera Menu

First, you’ll need to find your camera’s lens calibration adjustment setting in your camera’s menu. You should find it in the autofocus menu(s).

Different camera manufacturers have different names for lens calibration in their menus, so you’ll have to look for the right one.

Here’s how it’s referred to on the most popular camera brands:

1. Canon – AF Microadjustment
2. Nikon – AF Fine Tune
3. Sony – AF Micro Adjustment
4. Olympus – AF Focus Adjust
5. Pentax – AF Adjustment

Calibrating a Lens with a Focus Test Chart

One of the things you’ll need to calibrate your lenses is something that functions as a focus test chart. While you can make and/or download one and then print it out for free at home, you’ll still need to get the angle correct when mounting it.

If you don’t want to fuss with all of this, you can buy an inexpensive ready-made focus test chart. This really is the best option for those who don’t want to fork out the money for expensive software but don’t mind spending around $40 for something pre-made and ready to go.

The following instructions are for the Vello LENS-2020 Lens Calibration tool, but the principles work for any lens chart (as long as it’s at the right angle).

Step 1 – Assemble the lens chart (the Vello lens chart takes about one minute)

Step 2 – Choose a bright and evenly-lit area. Place the lens tool on a flat surface or attach it to a stand. Make sure it’s leveled. (The Vello lens chart has bubbles to help in leveling.)

Step 3 – Set your camera on a tripod and make sure it’s level and in-line with the target. The target should be situated at a distance of around 50x the focal length of the lens from the camera.

For example:

• 16mm – 0.8m / 2’7″
• 24mm – 1.2m / 3’11”
• 50mm – 2.5m / 8’2″
• 70mm – 3.5m / 11’5″
• 200mm – 5.5m / 18′

(Ignore the crop factor here.)

Step 4 – Set your camera to “center focus point” and the aperture to its widest setting, then adjust the shutter speed accordingly for a proper exposure.

Step 4 – Focus on the center of the target and take a photo.

Pro tip: Switch your camera to manual focus (both with the lens and the camera). Defocus so the line goes blurry, then switch it back to autofocus, so it will try to focus on the line.

Step 5 – Take a look at your image under 100% magnification. The intersection between the target and the ruler (at zero) should fall in the center of your depth of field. 

If the focus falls in front of the 0 (front focused) or behind it (back focused) then you’ll need to make some adjustments.

Step 6 – Go to your camera’s AF Fine Tune or AF Micro Adjustment menu. If you’re using the Zello Lens Calibration tool, the ruler marks should coincide with the offset steps in the menu setting.

Step 7 – Take another shot and verify that the focus is accurate.

Most photographers feel that this method for calibrating lenses strikes the best balance between DIY methods (like the one below) and expensive computer software.

Calibrating a Lens with a Ruler

The best DIY method (i.e. without buying a calibration tool) is done with a ruler and a white piece of poster board.

It’s not necessarily as accurate as using a lens calibration tool, but it works well enough if you truly want a free option.

Here’s what you’ll need:

• a low table
• whiteboard (you can also use white paper, though this is harder to keep motionless)
• 1-2 ruler(s)
• a camera on a tripod
• a pen

Step 1 – Attach a piece of whiteboard to a low table or another flat surface. Make sure the whiteboard is firmly attached and won’t move if accidentally bumped.

Step 2 – Draw a thin, clear line on the whiteboard/paper. This will give the camera a specific focal point with nothing else in the frame.

Step 3 – Set your camera on a tripod and make sure it’s level and in-line with the target. The target should be situated at a distance of around 50x the focal length of the lens from the camera.

For example:

• 16mm – 0.8m / 2’7″
• 24mm – 1.2m / 3’11”
• 50mm – 2.5m / 8’2″
• 70mm – 3.5m / 11’5″
• 200mm – 5.5m / 18′

(Ignore the crop factor here.)

Step 4 – Set your camera settings to the widest aperture your lens will go to and adjust your shutter speed to ensure a correct exposure. Then, select “center focus” and focus in on the line that you drew.

Pro tip: Switch your camera to manual focus (both with the lens and the camera). Defocus so the line goes blurry, then switch it back to autofocus, so it will try to focus on the line.

Step 5 – Place a ruler (or two) alongside the line. one, maybe two rulers perpendicular to that line. Line it up on a particular mark. One ruler will work fine, but many find that working with two rulers is easier. (Below you see two rulers using the 20cm mark.)

Pro tip: Make sure that nothing is going to move, neither your whiteboard, your rulers, or your camera.

Step 6 – Take a photograph and examine the results.

The sharpest number should be the one that aligns with the mark. In this case, that should be the 20cm mark, but as you can see, the 21 cm mark and even a few notches towards the 22 are sharper than the 20.

If the results are off, go into the menu and find your AF micro adjustment feature. Choose “adjust by lens.” You should see a scale that allows you to fine-tune for both front-focusing and back-focusing.

In this case, my lens is back focusing (sharper away from the camera), so I’ll need to move the adjustment line towards the negative side of the scale.

To compensate for the back focusing, I moved the adjustment mark to -10.

Step 7 – Take the shot again and compare the results. Make any further adjustments necessary. The goal is to have the number aligned with your focal point be the sharpest. (Here it’s the 20cm mark.)

Calibrating a Lens with Software

For superior results, you can always invest in lens calibration software. The most popular is Reikan FoCal.

At just under $60 for the Plus version and over $130 for the Pro, it’s not cheap. Also, it doesn’t work with all cameras.

That being said, there’s something to be said for a fully automated process that’s quick, easy, and you don’t have to worry about user error.

That being said, not every user has successful results with lens calibration software. Many users report software compatibility issues and complicated instructions.

Step 1 – Attach the target to a wall. (Most lens calibration software options will include either a hard target or a downloadable target for you to use.)

Step 2 – Put your camera on a tripod at a distance from the target that’s 50x the focal length of the lens.

For example:

• 16mm – 0.8m / 2’7″
• 24mm – 1.2m / 3’11”
• 50mm – 2.5m / 8’2″
• 70mm – 3.5m / 11’5″
• 200mm – 5.5m / 18′

(Ignore the crop factor here.)

Step 3 – Attach your camera’s USB cable to your computer. Turn your camera on and switch it to Live View mode.

Step 4 – From here the software should take over.

How do you Calibrate a Zoom Lens?

Calibrating a zoom lens is a little trickier – at least on most DSLRs.  A few of the more recent Nikon and Canon DSLRs allow for “two point” lens calibration, but the majority of cameras only support a single micro-adjustment setting for each lens.

Since many zoom lenses vary between zoomed in and zoomed out, with the zoom extremes showing the greatest difference.

Note: For a list of Canon and Nikon cameras that support two-point lens calibrations, look on the Reikan FoCal Supported Cameras page under “Wide and Tele Calibration.” 

If your camera doesn’t have a “two point” adjustment available, bias the adjustment towards the telephoto end of the range. (Focus errors have a greater impact at the telephoto end.)

Final Words

If you shoot with a DSLR and need your images to be tack sharp, knowing how to calibrate your lenses will be a critical skill.

It’s nothing short of disappointing to spend a bunch of money on a fine, reputedly sharp lens, only to get less than sharp images coming out of it.

What do you think? Ever used the AF fine-tune feature? Do you calibrate your lenses? If so, which method do you use?