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
if it doesn't lock AF on any scene then it is likely there is a fault
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