When we finally pluck up the courage to purchase an expensive lens, we expect them to be perfect right? Unfortunately, no matter how good the lens is, there are always going to be minor differences when we attach it to our specific camera. Often our camera bodies are made at a completely different time and usually in a completely different factory, so when we finally bring the two together there are often minor adjustments that we the user have to make to ensure we're getting the best Image possible from that specific lens.
So regardless of whether our lens is new or old, or if our camera body is new or old, many will say fine tuning your lens to your camera body is crucial.
How to Calibrate your Lens
Thankfully calibrating your lens isn't difficult and if you're going to do all of your lenses at the same time, it shouldn't take more than a couple of hours to do them all. It's worth pointing out now that this process is really to calibrate the autofocus on your camera to the desired lens and will not fix ‘soft’ focus lenses in any way. If your lens is soft when you manual focus with it, this process will not improve it.
What you will need:
Focus chart or ruler
Software to review results
Patience of a saint
Set your tripod and camera up at the same height as your chart or ruler and make sure the camera is level. Use a spirit level (usually on most tripods) if necessary.
Setting up your chart
Next you’ll need to set up your focus chart. Although there are plenty of places online where you can download and print out focus charts, I personally don’t feel it’s all that necessary. I used a metal ruler that I had in the drawer and that seemed to work for me. In fact you could just as easily use some packaging that has a lot of text on it. The real trick here is to mount the focus chart/ruler at an angle so you can see the focus drop off. You just need to have a specific point to focus on and then other areas of detail around it to see where the actual focus is falling. Like I said, I used a metal ruler as I could focus on a specific measurement number and then check what was in or out of focus around it.
I mounted mine on a stand at a downward angle and focused my camera halfway along the ruler.
Setting up your Camera & Tripod
Next up we’ll need to make a few adjustments on our camera setup and settings.
First you’ll need to place your camera and selected lens at the appropriate distance from the ruler. This distance is dependent on the focal length of the lens you’re calibrating and the easiest thing to do, is check the details on this super handy chart from LensAlign. Their Distance Tool allows you to input your camera sensor size, your focal length and minimum aperture and it’ll give you the optimum distance you’ll need to do the test. Input your numbers and then set up your camera at the appropriate distance as recommends by the site.
You’ll want to set your aperture to the widest your lens will allow. For example in this instance I was calibrating my 50mm f1.4 lens so I set my cameras aperture to f1.4. Make sure you have adequate ambient lighting and that you’re shooting at a fast shutter speed to capture a very crisp image to avoid minor movement throwing off the focus adjustments. I had my ISO at 1600 as the noise wasn’t a concern because I wasn’t interested in printing these out.
Next you’ll want to switch to live-view to enable you to zoom in and really nail the focus. It’s my recommendation that you should select the centre focus point as well as choose the smallest focal point possible.
Once all that is done, it’s time to zoom in and focus on the centre of the ruler and take a shot. Again, my advice would be to take at least three shots here so that you can get a broader look at the auto focus. Each time de-focus the image and then refocus again to test the auto focus properly.
Importing and Checking your Images
All that’s left to do now is import your photos into editing software like Lightroom or Capture One. Importing your photos into an image capture software enables us to zoom in a lot further than on the back of camera. Remember that the image on the back of your camera is a JPEG so zooming in a long way can make the image appear fuzzy, whereas importing them into software like Lightroom allows us to check the focus point accurately. Once you have imported your photos, zoom into the image so that the focus point is filling the frame. Now we can assess whether there is any fine tuning to be made with our autofocus.
Sometimes it can be hard to distinguish what is in focus and what isn't, so a good trick can be to use the colour picker and see what colours appear in the focal range. For example most lenses will have aberrations and those aberrations are consistent in a digital file. Areas that are out of focus behind the focal point tend to have a green hue to them, and areas that are out of focus in front the focal point tend to have a magenta hue to them.
Making the Corrections
First off we’ll need to bring up our AF-Fine tune to turn it on and make the adjustments. This is the Nikon menus but the other cameras use a very similar name and process. For Nikon go to the menu with spanner icon and in there at the bottom you have the Af Fine-Tune Menu. Go in there and then turn on the AF-Fine-Tune.
I had a quick look for the Canon version and you can see how to access it here Canon AF Fine tune
So now that we have our AF Fine-Tune enabled, we can begin to make some adjustments. If we look back at our imported images and review them to see what can be improved.
If you feel that the cameras autofocus is missing the mark consistently, then you'll need to make some adjustments in the fine tune menu of your camera. So for example if your autofocus is consistently focusing behind the intended focal point, you'll need to adjust the autofocus fine tune with minus numbers to bring it back to where it needs to be. Conversely, if the autofocus is consistently focusing just in front of the intended focal point (closer to the camera), you'll need to increase the autofocus fine tune with positive numbers.
For example in the image above you can see my 28 to 105 mm Lens was consistently back focusing, which meant that the fine tuning adjustments ended up being -13 in the fine tuning menu. This process can take several attempts to get it perfect so you may want to make large changes to begin with to start seeing the effect. Make the fine tune adjustment, take some more shots, review the images in Lightroom and make any necessary adjustments again. Repeat the process until you're happy.
It’s highly likely that you’ve read the procedure of how to calibrate your lenses before you’ve actually gone ahead and implemented the process for yourself. So before you dive in and start this admittedly mind-numbingly boring process, let me just warn you that this is not the holy grail of razor sharp images but merely a single step in achieving them. It’s also worth mentioning that this process only helps to get sharper auto-focus shots, it does not make the lens itself any sharper. If you wanted to test this further to see just how sharp your lens is then I recommend you use live-view, zoom in to max and take some manual focus shots just to see how sharp your lens actually is a reference point for the auto-focus tests.
Do I really need to calibrate the fine-tune of my auto focus?
My basic answer is no, I personally don’t feel this is necessary for most portrait shooters, or street shooters or in fact most shooters that are not using a tripod most of the time. I think if you’re a landscape, wildlife or still-life shooter then this is probably worth your time to do as critical focus is often crucial for what you do, but more importantly, achievable.
For those of us shooting portraits or fashion or just people in general, I don’t think you’d notice the adjustments being made here. These are micro adjustments remember, and hard to spot consistently even to the trained eye. Plus the adjustments are barely noticeable in a very controlled situation with the one specific goal is to spot these variances. There is very little chance that whilst we’re handholding a camera and taking a picture of another moving subject with focus and recompose variations that you’d notice these fine-tune adjustments.
Should you calibrate your auto-focus on all of your lenses the next time you have a spare afternoon?
Sure, it can only help.
Should you go out of your way to make calibrating your lenses a priority before you take another photo?
No I don’t think so.
BONUS TIP FOR NIKON SHOOTERS
Did you guys know that us Nikon shooters have a shortcut through this whole lens auto-focus calibration process, that allows the camera to read an image and make micro adjustments automatically?
Well rejoice because most modern Nikon camera now have this rather hidden feature and here’s how you activate it.
I honestly have not looked to see if this is possible with other brands like Canon and Sony so if you know it can be done with those brands, please let me know in the comments.
Setup up your shot like we mentioned before. In fact it can be any object that is fixed in front of your tripod. Activate live view, zoom in all the way, use single shot auto focus and select the smallest focal point you have.
You don’t actually have to take a shot as the camera will do that for you in the next step. What you need to do next to hold the auto-focus selection button (often located on the auto and manual focus switch) and the video record button for about 3 seconds.
If done correctly a window will appear asking if you’re sure. Make sure you’re firmly planted with a tripod as it suggests and hit ‘Yes’. I actually recommend very lightly touching the screen (if you have a touch screen Nikon) to confirm this as any camera movement during the process will not allow you to proceed.
If everything was done correctly, your camera will then show you another screen a couple of seconds later to say “The new value has been added to the ‘AF fine-tune’ ‘Saved value’ list.
You can now go to the fine menu and see what value has been assigned to you lens to correct it.
Although this is an automated process, I strongly recommend you run this process several times as each time you will like get a different value assigned to the lens. Remember this is far from an exact process so this was to be expected. The best solution I found was to simply take an average of several readings. So for example I ran the same process 5 times on my lens and here’s readings I got: -16, -15, -19, -13, -14. I just added them all up and divided it by 5 to get the average and then input that number as the best value.
Auto AF fine-tune failed.
You will likely get the auto AF failed window a few times and here’s a couple of things I did to fix the issue.
Make sure there’s enough ambient light. If not, don’t be afraid to boost the ISO.
Shutter speed to low. - I was originally shooting at a 60th but it needed a faster shutter of 125th to work in my tests.
The camera moved. - Like I mentioned before, when the screen pops up asking if you’d like to proceed, be as gentle as possible to avoid any subsequent camera shake.
Improper source image - The image filing the focal point needs to have sufficient detail for the camera to look at. Mine had strong lines but text on a non-shiny surface would work well too.
Thanks for Reading
Well there you have it guys, I hope this was useful and at the very least it’s given you some knowledge about the process.
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