Usually, turning the camera off mid-shot is unlikely to physically damage the camera, but it can interrupt the exposure or corrupt the image being recorded.

Key issue: power is needed for the sensor, shutter timing/electronics, autofocus, and especially for transferring image data from the buffer to the memory card. If power is cut during that process, the current photo may be lost or unreadable.

Many camera manuals specifically warn not to switch off the camera while the card-access/write light is flashing. More sophisticated cameras may ignore the power-off request until buffered images finish writing, but that behavior depends on the model.

So:

• During a long exposure: turning off may stop the exposure and lose the shot.
• During autofocus: behavior depends on the camera, but it generally won’t help and may interrupt operation.
• While writing to the card: avoid powering off, since the image file may be corrupted.

Best practice: wait until the exposure is complete and the write/access light has stopped blinking. Check your camera manual for model-specific behavior.