A Guide to Solving Autofocus Problems
On this video wildlife and nature photographer Steve Perry (from backcountrygallery) looks at some of the most common auto focus problems that you might encounter when shooting and how to resolve them.
AF issues are responsible for at least some of our images which we might consider not sharp (there are of course other issues such as physical problems with our lens, too slow shutter speed etc.) but AF problems are things that you need to be able to eliminate as much as possible.
Here are the 8 main ones Perry discusses in this video:
- AF fine tune – in some cases it is possible that the lens-camera combination you are using isn’t calibrated correctly – most semi-pro and pro cameras have the option to fine tune the AF (and now both Tamron and Sigma have USB units which allow to do this calibration without the camera with some of their new lenses). Here is the link to the Dot-Tune method video which Perry mentions in the first part.
- AF sensors on your camera are dirty – This is something you might not have considered. We might think that are lens is dirty, we can even consider that our main camera sensor is dirty but the AF sensor? well, yes. These are usually below the mirror – you can clean them with a rocket/pocket blower that you are using to clean your main sensor. Follow the steps that Perry suggest including putting your camera in a cleaning mode so that when you tell your mirror to go up it won’t come down accidentally on the tip of your blower.
- Wrong AF mode is selected – You need to realize which AF mode to use for which type of shot. Typically you would want single AF (AF-S in Nikon or One-Shot AF in Canon) mode for stationary or almost stationary subjects and continuous (AF-C in Nikon or Servo in Canon) mode for tracking moving subjects. There are more to AF modes than just AF-S/AFS-C (if you are a Nikon shooter you simply have to watch Perry’s video on “Understanding and Using Nikon AF Modes” which we covered here some time ago.
- AF outline guides in your camera are not accurate – the little red rectangle that shows you where the “active” AF point is – is just a rough guide – Perry shows in the video how to test how close it is to where the actual AF points are – if you have a problem here – you might need to send your camera to be corrected in the lab.
- Fighting heat refraction – when you are shooting with long telephoto lenses – especially on hot days – heat from the ground changes the air density and the longer you shoot the bigger the problem. The only solution is to move to a less warm area of to get closer to your subject (not always possible but just be aware).
- Dirty contact on the camera or the lens – this is another physical issue that might cause problems with your AF performance – clean with either 99% alcohol or something like the DeoxIT DN5 Mini-Spray – be careful and follow Perry’s instructions here.
- Poor technique – The main problem here (which we actually mentioned above) is a shutter speed which isn’t fast enough to freeze the movement of your subject. We tend to underestimate just how fast we need a shutter speed to be to freeze action – try pushing the shutter speed up and see if this helps. Of course you might not be stable enough – either get a better tripod or improve your hand-holding techniques.
- Not all AF sensors are created equal – typically the center AF sensor (or in higher end modern cameras “sensors“) are more accurate and sensitive and can focus in lower light – if you struggle with AF – try using the center point and see if this helps.
If you liked this video there are two other video by Perry which you might want to watch – “How To Use AF-On And Back Button Autofocus” and “Super Tip: Manual Mode With Auto ISO“. We can vague for both videos and we have been using the techniques Perry suggest for quite some time with great success so give them a try and see if they work for you.