My dad has a Nikon D90, and we were out taking some pictures last night. He's complained about the camera "randomly" refusing to take a picture before. My theory was that it was because his focus was set to AF-S, but I didn't shoot with it enough to know.
However I did set it to AF-C and started shooting and noticed that there was about a half-second delay between pressing the shutter button and the camera firing. Things that may be noteworthy:
- No, the self-timer wasn't on. It was for a moment and caused a 2s delay, but we fixed that :)
- It's set to use back-button focus (AE-L/AF-L is set to AF-ON)
- Flash was set to auto (and popped up, as it was dark)
- Shutter speed was 1/100
- ISO was 800
- Exp. delay mode is OFF
I thought that it could be the flash charging, but it still happened after waiting a few seconds in between shots. Even the flash charging indicator stopped blinking.
One thing I just noticed sitting here trying to reproduce the behavior - it seemed like a half-press while the flash was charging would not allow me to take a picture after the flash finished charging, but repeating the experiment I couldn't get the behavior to repeat.