Tag Archives: Auto focus

Auto focus blues & how to cure them

Canon’s DSLR cameras can be set to auto focus (AF)  or manual focus (MF). The auto focus setting is very convenient for photo booth operators, but when the camera cannot find anything to focus on it will not take a photo.

This post has been written for DLSR Remote Pro 3.7.3

What can go wrong using auto focus?

You may notice a long pause before the camera takes  a photo. The focus motor whirrs and the camera lens moves as the camera tries to focus. Two different error messages may be displayed: ‘Unable to release shutter’ or ‘Unable to focus’.

Unable to release shutter

When setting up the booth the operator presses Release(F8)  or Preview (F9) to check camera operation. No photo is taken and this error message is displayed:

Error message for DSLR Remote Pro 3.7.3 displayed: Unable to release shutter. This may be because the AF was unable to lock
DSLR Remote Pro 3.7.3 ‘Unable to release shutter’ error message

Unable to focus

After the countdown there is a long pause before the camera takes  the first photo. The focus motor whirrs and the camera lens moves as the camera tries to focus. Eventually this message* is displayed:

DSLR Remote Pro 3.7.3 error message 'Unable to focus! If you are standing close to the camera please try moving back a bit. The booth will retake the photo in ... seconds...
DSLR Remote Pro 3.7.3 ‘Unable to focus!’ error message *

*Hint (localization) You can translate this message into your local language using the PhotoboothAfErrorMsg message in the configuration files

Why does this happen?

Usually the camera cannot focus because

  • there is not enough light
  • the booth is empty and has a plain background
  • guests are too close to the camera
  • the lens cap has not been removed

Autofocus works best with good lighting and guests positioned at the right distance from the camera. It may be improved by changing from a plain background. The most reliable solution is to switch the camera to manual focus.

How to make sure the camera will fire: Set the camera to manual focus

Exception : cameras with dual pixel AF. If your camera has dual pixel AF please see the Camera Settings section of the program help files. (At present the Canon EOS DSLR cameras with dual pixel AF are the Canon EOS 800D/Rebel T7i, 200D/Rebel SL2, 70D,  77D, 80D, 7D Mark II, 5D Mark IV and 6D Mark II*.)

*Support for the EOS 6D Mark II will be added to the next release of DSLR Remote Pro.

Simplest way to set the camera to manual focus

  1. Set the AF/MF switch on the camera lens to the MF (manual focus) position.
  2. Each time you set up the booth turn the focus ring on the camera lens until you see a sharp image on the PC live view display.
Photo of Canon REBEL T5 camera how how to switch between auto and manual focus
Canon REBEL T5 (1200D) showing AF/MF switch
Photo by Kārlis Dambrāns (edited to highlight AF MF switch)

Photo sourced from Flickr

Use the camera controls to set manual focus

Use the screen on the back of the camera to set the custom function “C.Fn IV: Operations/Others – Shutter/AE lock button” to “1:AE lock/AF” (refer to your camera manual if necessary).

Canon 200D camera display showing Customer Function IV
Customer function IV screen on Canon EOS 200D camera

This setting has the advantage that focus can still be adjusted remotely from the PC but auto focus won’t be used when taking a photo. The lens can be focused in fullscreen photobooth mode by typing Ctrl+A.

For more precise control of focus exit photobooth mode and type Ctrl+L to display the live view window. Then use the <<<, <<, <, >, >>, >> buttons or the mouse wheel to manually adjust the focus.

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