Imagine a terrible situation, you bought a new reflex camera, and the pictures that you take are not sharp. However, if you look at the pictures more closely you will find that the camera is focused but completely on a different object, not the one that you focused. The focus in such cases goes back to the background (if it’s beyond the object, then its name is “back focus”) or vice versa, closer to the foreground (if it’s in front of an object, then it is called “front-focus”). Both of these phenomena people usually call with the same term “back-focus”, because even if we consider that they are in opposition to each other, in fact, they all remain the same phenomenon, because autofocus missed the focused area.
Of course, such problems can be because of other reasons too. For example, focused object or camera could move etc.…
But if the problem is regular, it is worth contacting the service center for a procedure called “Focus Calibration” or try to do it yourself.
What is back focus?
Back-focus is a consequence of the inconsistency work of different camera systems.
This is usually linked to a problem with electronics and the problem may be within the camera, lens or a both of them.
Sometimes with some lenses, the phenomenon is noticeable, but not with other lenses. However, this does not mean that the first lens was a bad one.
How to check back or front focus issues and calibrate the lens
You need a printed focus chart, good tripod, enough place and lightness.
It’s better to do it outdoors, because there is a lot of light available.
Here are 5 steps, which you need to do for checking and calibrating your back or front focus.
1. Print the test chart in A4 paper, then put it somewhere in 45 degree like its shown in Figure 1. The height should be the same as your camera height.
2. Then put your camera on a tripod and make sure that your camera is parallel to a focus chart. Distance between camera and focus chart depends on the lens you are using. For example, for 50mm lens in full frame DSLR camera the distance should be approximately 1,5 – 2 meters. If you are using wider lens it should be closer, if longer then further from focus chart.
3. Set your camera in Aperture Priority mode and put in a maximum wider aperture (example: if you have 50mm F1,4 lens put F 1,4). Also its best to use self-timer mode for releasing camera.
4. Turn off image stabilization or vibration reduction mode in lens if you have it.
5. Use only single center focus point of your camera to focus and make sure that the lens is pointing at center of a focus chart.
6. Turn on Auto Focus of your lens and focus on thick black line in the middle of focus chart and take a couple of pictures.
7. Check the test photos in your computer monitor at 100% magnification to see if you have back or front focus.
8. To calibrate the lens For Nikon Cameras go to menu called ‘AF fine tune’ for Canon Autofocus Microadustment’
Enjoy your sharp images!