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How Do I Test My Camera For Autofocus Issues?

You might find your images are less than perfectly focused. You might have just missed the moving subject, or the light was too low for your camera’s autofocus to work.
If this is a recurring problem, then the problem lies elsewhere. I regularly test my camera and lenses for focusing problems, and you should too.
For all the information on how to do this, read below.
A person holding up a pair of glasses to an opticians eye chart - autofocus issues

Why Do I Need to Test My Camera?

With old age, our eyesight might start to fail. A trip to the opticians has us sitting in front of a chart 6 meters away. Blurry vision is corrected with the use of curved glass or plastic, fixing the light rays to focus properly.
Camera lenses also need help, either from the get-go or from constant use. Your images are only focused if you use your camera properly, and if you are, then there is an issue with your autofocus.
You need to make sure your camera autofocus is up to scratch to ensure your images are in focus. It’s that simple.
In our other article Simple Guide to Lens Calibration, we talk about how even new lenses need tweaking. This is a simple fix, and what we plan on showing you today is also the same.
This is the quickest and easiest way to test if your DSLR has an autofocus issue. You can use this for both front and back focus issues with any lens or camera body combination.
The camera I will be using is the Canon 5D Mark III, but any modern DSLR with live view will work.
NB: What we want to try to ascertain is if there is a problem that can be fixed by you, or it needs to be sent away for repairs. 
A person holding up a camera lens to an opticians eye chart - autofocus issues

Step 1 – What You Will Need

For this test you need:

  1. Any DSLR but it needs to have a Live View mode such as the Canon 5D Mark III or Nikon D3500.
  2. At least one lens. Use more if you want to autofocus test them, and pinpoint the problem to the camera body.
  3. A stable tripod.
  4. A flat, vertical surface in a well-lit area. An inside wall next to a window will work well.
  5. A focus chart. You can print out the Star Focus Chart or the Focus Test Chart on A4 size paper. Feel free to print it using an inkjet or laser printer. Don’t use anything glossy such as photographic paper.
  6. Sellotape, scotch tape or Blutack. Anything to hold the focus chart on your chosen surface.

A DSLR camera set up on a tripod - test my camera for autofocus issues

Step 2 – Setting Up

  1. Place your camera on the tripod, directly in front of a wall. Ensure the camera isn’t tilted in any way. Have the camera point directly at the chart at the same height.
  2. Hang the chart on the wall, opposite the camera. It needs to be vertical and straight. The height of the chart needs to be the same height as the camera and lens, so don’t hang it too high.
  3. The distance between your camera and the wall depends on the focal length of your lens. If you are using a 50mm lens, then you should keep between 5-7 feet. A wide angle lens will need a shorter distance and a telephoto lens needs a longer one. The aim is to fill around one quarter to a third of the viewfinder.

Step 3 – Camera Settings

When you find yourself testing the autofocus accuracy, you need to have consistent exposure.

  1. Switch to Manual focus mode and keep the same exposure for each shot.
  2. Set the lens aperture to its maximum or widest. For example, if your 50mm lens is f/1.8, set it to f/1.8.
  3. Set your ISO to 100.
  4. Use the Exposure Value to set your shutter speed. You need a well-lit environment to ensure your shutter speed is over 1/250. Anything below this could have accidental camera shake, rendering this test irrelevant. You won’t know if it is a focus issue or a camera shake issue.
  5. Ensure that AF Fine Tune/AF Micro Adjustment is turned off if your camera has it.
  6. Set the focus point to the centre focus point. The centre focus point is always a cross-type sensor, making it the most accurate.
  7. Turn off any sort of lens corrections in your camera, such as distortion or chromatic aberrations. There shouldn’t be anything affecting the test results.
  8. Set the camera to AF-S/Single Servo Mode.
  9. Shoot in Raw mode as cameras tend to add sharpening and colours to JPEGs.
  10. If your camera has a Live View mode named ‘Tripod’ – Use it.
  11. If your camera has a Mirror Lock Up feature, use it and a remote camera release. This will help to prevent camera shake, especially for slower shutter speeds. You can also use a timed exposure too.

Step 4 – Capture

Now that everything is set-up, it is time to capture some images. Follow these steps:

  1. Capture the focus chart in Live View mode. Turn it on, and zoom into the centre of the focus chart. Focus by half-pressing the shutter release button, or use your back-button if you use back-button focusing.
  2. Press the button and capture the image.
  3. Analyse the image at 100% view and make sure it is pin-sharp in the centre. If it looks sharp, you did everything correctly. If it looks blurry, then your camera didn’t acquire focus properly.
  4. Take images until you get the sharp image.
  5. Next, take an image without using Live View. Turn off Live View mode, and un-focus the image using the focus ring while looking through the viewfinder. We want to force the camera to refocus.
  6. Half-press the shutter button to acquire focus. Take a test shot.
  7. Repeat steps 5 and 6 until you have three images that show the centre point in focus.

Why Do We Do This?

All DSLR cameras use the ‘Phase Detect’ autofocus sensor located inside the camera. This system works very fast, however, they need to be properly aligned and calibrated for it to work.
We are testing that system in our methods above. When we use Live View, the mirror inside the camera flips up. This stops the Phase Detect system from focusing. Instead, ‘Contrast Detect’ acquires focus.
The camera forces the lens to focus back and forth until the image looks sharp. This method is much slower in comparison. Because focus confirmations happen electronically, they are always accurate.
Our Live View image is our reference image.

Step 5 – Analyze

Now that we have a sharp reference point and other images, it is time to analyse our captures. Load the images into your post-processing tool you of choice. Open the first image and make sure it looks sharp in the centre.
It should look something similar to this:

Next, look at the other three images you took using the viewfinder. do they look more or less the same? Or so they look out of focus?
Here is an image I photographed with Contrast Detect, clearly showing a focus problem.

As you can see, not only does the image look out of focus, but it also has some aberration problems. All three images are similar, indicating a focus problem with either the camera or lens.
It is very important to switch between your reference image and the second group of images. If things look out of focus, you need to start the process again.
You should be getting consistently good results or bad ones. If they are consistently good, then you do not have a focus problem.
If they are bad, then the next logical step is finding out if it is your lens or camera that has the problem.

Step 6 – Camera or Lens?

It is best to test multiple lenses when assessing the autofocus accuracy of your camera. If you only test one lens, it is impossible to know where the problem lies. It could even be both.
If you have more, perform the test using all the lenses you have. If every lens shows similar results, then the autofocus issue is with your camera.
Still, it is difficult to pinpoint the exact source, as your lenses would be very badly calibrated to start with.
The reason I was interested in writing this article was that I had no idea about calibration or testing my lenses.
Like many people, I imagined my camera and lenses were perfect from the moment I bought them. From research, I found this not to be the case.
I also started noticing how problematic one of my lenses is when used with my Canon 7D. Other lenses I use with it are tack sharp.
My 24-70mm lens has difficulty focusing perfectly, and I always imagined it was down to its quality or my imperfect focusing.
A blurry image of a neon sign reading 'focus'

Step 7 – How to Solve Issues?

So, what do you do if you find a focus issue with your camera or lens? Most people would take it back to the place where they bought it from.
There are return policies for this reason, but you don’t need to use them. For one, the item will be classified as defective, wasting valuable resources and time.
The item goes back to the lab, where they can’t find anything wrong with it, and then re-sold as refurbished. It can’t be sold as new.
On top of this, there is no guarantee that the lens or camera you receive as a replacement will be any better. It might actually be worse.
You might have to wait days for a replacement when you might not need to wait at all. The best thing to do is to take it to the manufacturer for repair or fine-tuning or try to calibrate it yourself.
Every manufacturer has dedicated support centers that deal with issues and defects, which would still be under warranty.
You can try to re-calibrate your lens. Read our Simple Guide to Lens Calibration to try and solve the issue yourself.

Recommended Approach

  1. Keep all of the images taken from your focus session.
  2. Contact the manufacturer’s service support team and explain the issue you are having. Provide the image samples to the service personnel
  3. Send them the faulty item, either the camera or the lens. Ensure they pay for shipping and insurance, which they should do if under warranty. If they refuse, be sure to speak to someone above them. Why should you pay for a defective item?

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