photo:diy_af_fails

troubleshooting: your camera is refusing to autofocus or images are blurry

The Problem

  • You half-press the shutter button to auto focus and nothing happens

Potential causes and solutions

camera tries to AF but fails

  • you are trying to focus on something outside the lens' focus range
    • in this situation you should hear the lens trying to find something on which to focus
    • all lenses have a closest focus, ensure your subject is further that this
    • some lenses have a focus limit switch to speed up AF - ensure this is set correctly for your subject distance
    • some cameras such as the Olympus OM-D E-M1 mark II allows you to set a focus range within the camera for any compatible lens - check you have not set this and activated it
  • ensure the subject or camera is not moving too fast
    • camera AF systems have a limit to how fast a subject moves before it fails to lock AF
    • this is particularly an issue with CDAF only camera focus systems such as in many mirrorless cameras, or in many dSLRs in Live View mode
    • keep the camera as still as possible
    • if subject is too fast resort to other techniques such as manual focus on the predicted distance
  • subject lacks contrast or lines
    • again,this is particularly a problem with CDAF only cameras, but may cause issues with PDAF sytems too
    • try locking on a more contrasty region at same distance and recomposing
  • subject is too dark
    • try shining a torch or activating the AF assist beam
  • the subject is too small
    • many cameras will have trouble with locking focus on very thin or small subjects such as a single thin flower stem
    • try using “pinpoint AF” mode if available, otherwise consider using magnified mode then AF, or try locking AF on the base of the stem where there is more subject matter, and then re-composing
  • backlit subjects
    • these are often very troublesome for camera AF systems whether CDAF or PDAF
  • if using a lens adapter, it may not have AF compatibility
    • an example, is the Sigma Canon EF adapter for Sony cameras, many Canon lenses will not AF correctly
  • camera or lens is faulty

camera locks focus but images are blurred

  • camera has locked AF on a different part of the image
    • check your AF region / active AF point
    • avoid using all area AF as this tends to lock focus on closest contrasty subject - it is best reserved for situations without foregrounds
    • take care with face AF/Eye AF, as ithe camera may lose AF lock on the eye or face if subject turns away or moves, in which case it will default to the active AF region/AF point which may not be where your subject is
  • subject has moved after the AF was locked
    • a common issue if using Eye AF or CDAF only cameras with C-AF mode
    • if using Olympus cameras sometimes S-AF mode without Face/Eye AF gives better results if the subject is moving
    • if using the E-M1 Mark II then C-AF modes work very well
  • misalignment of AF system
    • this is mainly an issue with dSLR cameras
    • the issue arises as dSLRs have a separate sensor for PDAF autofocus and very slight physical distance changes can result in a lens locking in focus at a slightly too close or too far position, resulting in every inage not being sharp
    • most dSLRs have a AF MicroAdjustment procedure to allow one to manually correct this for EACH lens
    • it is rare for a mirrorless camera to require this as their AF sensor is on the same sensor used for recording the image
  • all parts of the image is blurred due to subject or camera movement not AF error
    • check your shutter speed and image stabiliser setting
      • remember that to activate IS you may need to ensure IS switch on the lens (if there is one) is set to ON AS WELL AS the IS setting within the camera
    • you may need to either:
      • use a faster shutter speed by raising ISO or using a wider aperture (and/or remove any ND or polarising filter)
      • use a flash
      • resort to a tripod
      • use electronic first shutter mode
        • many cameras have a problem with the first shutter activation causing “shutter shock” which may cause blurring of images at shutter speeds slower than 1/320th sec - in this case, consider using 1st shutter electronic shutter mode if this is available
      • use mirror lockup mode
        • dSLRs may also suffer substantial camera shake from the mirror - if this is a problem, use a tripod and lock the mirror up and either use a self-timer or a remote control to activate the shutter
      • pan the camera with the action

camera does not even try to AF

  • camera is unresponsive
  • if using a lens adapter, it may not have AF compatibility
    • an example, is the Sigma Canon EF adapter for Sony cameras, many Canon lenses will not AF correctly
  • camera is not communicating with the lens
  • you are using a manual focus only lens
    • this should be pretty obvious
  • you have de-activated autofocus
    • you may have done this accidentally on the camera lens:
      • some lenses have a MF-AF switch
      • some lenses, mainly some Olympus lenses, have a MF clutch - ensure the manual focus ring is pushed away from the camera to activate AF
    • you may have done this in the camera settings
      • check you camera's status display
  • you may have set the camera to “back-button” focus
    • a common pro technique is to de-activate the shutter release button from AF duties, and to re-assign this to a button on the back of the camera
    • check your camera's menu settings
  • camera or lens is faulty
    • if all else fails, it might mean a trip to the repair shop
photo/diy_af_fails.txt · Last modified: 2017/11/06 11:21 by gary1