How to Test Your Camera’s Auto Focus System
Let’s say you are having a focusing problem with your DSLR and after careful consideration, you’ve come to the conclusion that’s it’s not you causing the blurry images you’re getting. You’ve done everything right and you feel there could be an issue with your auto focus.
Well there is one way to find out and if this does not pan out, then you know you have to go back and review your copy of basic photography 101. If you don’t have one,
then you may want to consider a good class in basic photography. We all falter occasionally and come up with an image that is surprisingly “soft”, as professional photographers like to call it.
Not too long ago, although I would guess many young photographers are not aware, in the medium format film days of using Hasselblad and Mamiya cameras and lenses, their lenses were so sharp we would use either a soft focus or diffuse filter in front of the lens when doing a portrait or even some wedding images. This gave us a nice soft dreamy look.
With that said, there can be problems with your auto focus system. Now that we have very high resolution sensors, slight focus problems are much more noticeable than on low resolution sensors. Makers of high end DSLR are acknowledging possible auto focus issues and are now allowing owners to make fine tune adjustments in their menu.
Although unlikely, but still a possibility, if your lenses have focus issues with a certain camera body and are not present on a different DSLR body, then you might have one of those defective DSLRs that need to be repaired or re-calibrated by the manufacturer. A greater possibility may be the fact that most cameras and lenses are massed produced and still within acceptable tolerances but may not be a perfect match and could possibly be slightly out of calibration.
An easy way to test your auto focus system and even manual focus accuracy is to use a test chart. A popular Focus Calibration System among professional photographers is made by Michael Tapes and is called LensAlign® Focus Calibration System. This allows you to test your DSLR auto-focus performance and if necessary, you go into your
camera’s menu system and make the adjustment. Each camera manufacturer has it’s own name for it. Nikon calls it AF Fine Tune, Canon – AF Microadjustment, Sony – AF
Micro Adjustment, Pentax – AF Adjustment, and Olympus – AF Focus Adjust.
In a nutshell, the way Michael Tapes LensAlign® Focus Calibration System works is that you mount the camera/lens combination to be tested on a tripod that has a ball head or pan and tilt controls. LensAlign® can be table-top or tripod mounted with its 1/4-20 tripod socket. To illuminate the LensAlign® DOF Ruler use any diffuse light source that yields relatively even lighting without producing hot spots. Window lighting would work as would on-camera bounce flash. It is important that there is enough bright
light falling on the focus chart so that the auto focus can lock on. Be sure to set the shutter speed high enough to avoid camera shake.
While looking through the test camera’s viewfinder, adjust the camera’s position so the central LensAlign® Focus Pattern is aligned with the camera’s central autofocus zone.
Leveling your camera is easy, thanks to the patented leveling method that Michael Tapes developed you just align the red dots on the back of LensAlign® with the holes on the front.
Be sure you have your AF Fine Tune adjustment (On Nikon) turned off or set to zero before you focus on the test pattern. Make several exposures. Have a close look at them.
You can even view them in your camera’s monitor by zooming in to 100%, then rotate the rear dial and you will see one image after the other still on 100% zoom. Or, you can view them magnified in lightroom or photoshop.
Then you determine whether your focus is right on, front focusing (focus is in front of the mark), or back focusing (focus is in back of the mark). Here is where you have to play around a bit, test and re-test to determine the exact AF Fine Tune adjustment that you need. Say you have a bit of a back focus problem, then you go into your AF Fine Tune menu system and you may want to start by dialing in minus (-) 10 since you have a back focus problem. If your lens is focusing before the mark, then you have a front focus problem and you’re adjustment would be plus (+).
Once you make the necessary focus adjustment, lock it in and you’re set for this particular lens. If you have any other focus issues with other lenses, now is a good time to test, and if necessary, make the AF Fine Tune adjustment on them as well
The LensAlign® Focus Calibration System along with a complete user guide pdf can be seen at: http://michaeltapesdesign.com/lensalign.html or can also be ordered from
Amazon or B&H Photo.
Another excellent way of testing your auto focus system is to use Jeffrey’s Autofocus Test Chart from: http://regex.info/blog/photo-tech/focus-chart
This is the FREE chart I used when making a slight adjustment on my Nikon D7000 and Nikkor 70-200mm f2.8 lens.
To see how I used Jeffrey’s Autofocus Test Chart and made the AF Fine Tune adjustment, see the video below.How to Correct Focus Issues On Canon, Nikon & Other DSLRs (Short Version)
How to Correct Focus Issues On Nikon D7000, D7100 & Other DSLRs (Long Version)