CHECKING YOUR DIGITAL SLR CAMERA GEAR

How to keep your digital SLR camera in tip-top shape

How to identify autofocus issues of a DSLR or Lens

One of the first things you need to do after you purchase a new digital SLR camera and/or lenses is to check for auto focus accuracy. Even top brand manufacturers like Nikon and Canon have quality control issues and there is no guarantee that your brand new gear will be without any issues. The best thing you can do is to test your equipment as soon as you receive them and determine if there are any defects and return them for a replacement while it is still covered by a 30-day return policy.

One of the things that you can quickly do at home with ease is to check for auto focus accuracy. Autofocus issues can be caused by one of the following:

  1. A problem with the camera's autofocus calibration
  2. A problem with the lens calibration
  3. or, problems with both the digital SLR camera and lens calibration

What you need to do the Autofocus Test

So let's get right to it. Here's what you need to do the auto focus test.

  1. A focus test chart. This site has a good test chart you can use - http://focustestchart.com/focus21.pdf
  2. Your Digital SLR Camera.
  3. At least 2 lenses but if you only have one, that is ok.
  4. A good, sturdy Tripod
  5. Remote shutter release if you have one. This is to eliminate blurry test pictures. It is imperative that you are able to get the sharpest test picture as much as possible.
  6. If your camera can shoot in RAW mode, use this mode because JPEG pictures from your camera usually have sharpening algorithm already done on the image. As much as possible, we want to see your test image without any post-processing done like sharpening the image.

Preparing for the Autofocus Test

Before you can begin your testing, I highly recommend the following preparations:

  1. Pick a place (indoors) where there's plenty of available light.
  2. Set your camera Autofocus to ON. If your lens has both auto and manual focus settings, put your lens mode to Auto focus.
  3. Use the widest aperture of your lens. For example, if you have a 50mm F/1.8 lens then set your aperture to F/1.8.
  4. Set your camera to Aperture Priority Mode.
  5. Metering: Average metering mode (called Matrix for Nikon). Centered metering mode is also acceptable.
  6. ISO setting: ISO doesn't matter as much but try to get it at 400 or below. If you have plenty of available light then you shouldn't have any issues with this.
  7. Shutter speed: We need a fast shutter speed to eliminate any blur from camera shake. I would recommend shutter speed of 1/500 of a second or faster.
  8. If your digital camera has Image Stabilization or Vibration Reduction feature, turn these off. You don't need this because we will use a tripod.
  9. Set the focus point of your camera to the center focus point. If your camera has multiple focus points, make sure to set it to focus on a single point only and place to focus point in the center.

Autofocus Testing Setup Instructions

Ok, now we are finally ready to start testing. First off, print out the focus test chart you downloaded at http://focustestchart.com/focus21.pdf then follow the following steps.

Step #1: Aim your camera at a 45 degree angle from the focus chart. You can do this in one of two ways as shown in Figure 1 and Figure 2 below. Figure 1 shows the focus chart is angled at 45 degree with the camera shooting straight at it and Figure 2 shows the focus chart on a flat surface and the camera pointing downward at 45 degrees.

Setup Step 1
STEP #1: AIM YOUR CAMERA AT A 45 DEGREE ANGLE FROM THE FOCUS CHART

Step #2: Set a proper distance between your camera lens and the focus chart. Set your distance so that the test chart pretty much fills up the entire frame. If your camera does not focus at this distance then check your lens' minimum focusing distance and back up a little bit if you are closer than that.

Setup Step 2
STEP #2: OCCUPY THE ENTIRE FRAME WITH THE FOCUS CHART

Step #3: Focus your camera at the middle of the focus chart. There is a thick black line in the middle of the chart with a text that says "Focus here". Focus at this point.

Setup Step 3
STEP #3: FOCUS AT THE MIDDLE OF THE CHART

Step #4: Take a photo. Double check and make sure that your aperture setting is set at your lens' maximum opening. Also double check that your shutter speed is at least 1/500 of a second or faster. Take a couple of photos for good measure.

Step #5: Repeat the test using another lens. If you have more than one lens, it is advisable to do the same test on all of your lenses.

Step #6: Dowload your photos to your computer.

Checking your Results

Now that you have completed your test shots and have downloaded the test photos, you need to open and view them in your image viewing software. If you stored the images in RAW mode, use the appropriate image viewer. View the test photo at 100% magnification and check the sharpness of the image. Here's how you interpret the results.

THE IDEAL RESULT

Ideal Test Result
IDEAL TEST RESULT

Your ideal test result should show an image that is sharp in the middle (where you focused your camera) and then it gradually goes out of focus equally above and below from the middle. In the sample result image above, the image was taken using F/1.8 aperture - the middle is sharp and it slowly starts to blur just above the 6mm mark both above and below the center line.

THE ACCEPTABLE RESULT

Ideal Test Result
ACCEPTABLE TEST RESULT

The sample result above shows the thick black line (your focus point) is still sharp but it starts to blur at the 2mm below the middle while above the middle line it doesn't start to blur until around the 10mm point. This is still an acceptable result as long as your focus point comes up sharp.

BACK FOCUS PROBLEM RESULT

Back Focus Problem
BACK FOCUS PROBLEM

Back Focus is a defect on either the digital camera calibration or the lens itself where the area in your photo that is sharp is actually behind the object that you were focusing on when you took the shot. In the example result photo above, the camera's focus point is the thick black line but the image that it produced had the sharp area at the 20mm mark above the focus point and the focus point (the thick black line) is actually out of focus. This is a classic back focus problem.

FRONT FOCUS PROBLEM RESULT

Front Focus Problem
FRONT FOCUS PROBLEM

Front Focus is the exact opposite of Back Focus. It is a defect on either the digital camera calibration or the lens itself where the area in your photo that is sharp is actually in front the object that you were focusing on when you took the shot. In the example result photo above, the camera's focus point is the thick black line but the image that it produced had the sharp area around the 20mm mark below the focus point and the focus point (the thick black line) is actually out of focus. This is a classic front focus problem.

Is it the Camera or the Lens?

If your tests come up with undesirable results whether it shows a back focus or front focus issues, how can you tell if the issue is caused by the lens or the camera itself? If you are testing with a single lens, there is no way to tell if the problem is in the lens or the camera. If you are able to test multiple lenses you can check for consistency in your results. For example, if all of your test results produced back focus problems then it may be an issue with your camera's autofocus calibration. However, this is just an assumption and there is really no definite way to tell. The best thing to do is to have your camera recalibrated either by a professional repair shop or your camera manufacturer.

What to do next?

If your tests come up with undesirable results whether it shows a back focus or front focus issues, you can do one of the following:

  1. If your camera or lens is still under the 30-day money-back guarantee then you can still return it for a replacement.
  2. If your camera or lens was purchased over 30-days then use your manufacturer warranty and return it to the manufacturer. Your manufacturer can then decide whether to repair or replace your gear.
  3. If your gear is no longer covered by warranty then there is still hope. If your camera has a function that allows you to fine tune auto focus then use that to adjust the focus. This feature is usually available to higher end models only.
  4. If you do not have any of the above options, well, you can sell your gear and get a good one OR just learn to live with it. :)