When I first started using a digital SLR camera, one of the most frustrating problems I often came across, was when my DSLR lens wouldn’t focus properly. Instead, it would constantly move in and out, not stopping to focus on any particular object. Over time, I noticed a pattern to this annoying problem. Listed below are numerous reasons for your lens auto focus to fail.
Reasons why autofocus won’t always work on a digital SLR camera?
- The first thing to check when your camera’s auto focus fails, is that you have your DSLR lens set on AF (auto focus) and not MF (Manual Focus). This may seem obvious, however there have been many times when I’ve used manual focus and forgot to change it back to auto focus when required. If you are able to switch between AF and MF, you will find the switch for this on the side of your actual lens.
- Auto focus may have trouble working properly in low light conditions. For example night shots.
- Many photographers find auto focus fails when photographing non contrasting subjects. For example, a cloudless blue sky or a wall that contains one solid color.
- Photographing highly repetitive patterns like skyscraper windows or cars with reflective bodies can also cause problems.
- Personally I find my lens sometimes has trouble auto focusing if I’m taking macro shots and the insect or flower is constantly moving. I’ve been assured by other photographers that this is normal.
- Focusing on overlapping objects can also confuse your lens. For example, if you are trying to focus on the horizon, or say an animal in a cage. Times like these can make it hard for your lens to clearly know what it is you are trying to focus on.
- Sometimes auto focus AF may not be possible if you have an Extender attached to your lens. Check your Extender’s instruction manual for lens compatibility. Any other lens add-on’s like magnification and closeup filters can also cause problems.
What to do when your DSLR lens auto focus AF won’t work?
- Sometimes it’s just a matter of focusing on something different. For example, in landscape photography (where you want everything sharp) it usually doesn’t matter if you set your main focus on the horizon, or the tree you see in the distance.
- Try focusing on an object within the same distance as the subject you are photographing. Then switch the lens to manual focus MF, recompose and take the shot.
- An alternative to using manual focus mentioned in the solution above, is to focus on an object within the same distance then use your camera’s ‘focus lock’ setting (check manual). Personally, I find it easier to simply switch the AF setting on the side of the lens to MF. Don’t forget to change it back again for your next shot.
- There are times when your only option may be to use manual focusing.
Photography Assignment – Grab your DSLR camera and give this a try
It’s important to practice alternatives to auto focusing, for times when your lens AF setting isn’t co-operating.
Assignment: A lesson in auto focusing and alternatives
- Attach an all purpose lens to your camera. Make sure you choose a lens that has an AF / MF switch on the side. Set the lens to AF (auto focus) to begin with.
- For this example, change your camera’s ‘AF Point Selection‘ (Canon) or ‘Focus Area Selection‘ (Nikon), so the middle focal point is the main focus. If you’re not sure how to do this, refer to your camera’s manual.To check if you’ve set this correctly, turn your camera’s mode dial to P (for program). Look through your viewfinder and focus on an object by pressing the shutter button half way down. You should see only the middle focal point light up. If more than one focal point lights up, or a different point other than the middle one, repeat this step.The image below is an example of a middle AF point selection, as seen through a Canon 400D. Depending on your camera brand and model, you may see more or less focal points. However many you see, make sure only the middle point is lighting up whenever you focus on an object.
- At this point you should have your camera dial set to P and your lens focus switch set on AF for autofocus. Aim your camera towards an object and press the shutter button half way down. When you see the middle focal point light up or blink, take the shot. You have now taken a photograph with auto focus turned on.
- Lets pretend for this example, that your camera had trouble focusing on the object you wanted to photograph. Look through your viewfinder and focus on an object within the same distance to the one you want to photograph. Now turn your lens AF switch to MF for manual focus. Aim your camera back to the object you want to photograph and take the shot. The difference being, this time no focal point will light up or blink. However, the image quality should be very similar to the first photograph you took in step 3. You have now taken a photograph with AF auto focus turned off.
The next time your camera has trouble autofocusing, you now know how to solve the problem.