I am afraid that EMDK for C (I did not check C#) seems to not support focus management:

Imager Capability IMG_ACQCAP_FOCUSLENGTH is said to behave as "Setting has no effect on the behavior of the hardware. The function returns success. Getting returns the last value set". Note that this is specific for taking pictures (image capture). However, if you meant using the camera as a scanner, int this case yes there is an option: In IMAGER_SPECIFIC structure, field dwFocusMode is as follows:

Focus mode to use. Possible values are: FOCUS_MODE_FIXED (=0) – Fixed focus. FOCUS_MODE_AUTO(=1) – Auto focus I never tried this, but you could try and "combine" Capture and Scanner settings for the camera. Of course it can not be opened simultaneously as capture and as scanner, so first open it as a scanner, disable autofocus, close it, open it as a camera and check if disabling autofocus persisted.