I am a beginner in photography and just bought a EOS 300. My question is about the camera's focusing mode.

In all the Creative zones, when I tried to focus, the camera drifts in and out of One Shot AF and AI Servo mode unpredictabily. Hence, some of my photos became out of focus because I did not notice a 2nd 'beep' just before the shutter release when I re-compose my shots.

This is very annoying.

Later, I read that by pressing the DOF button, the camera will be forced into One Shot AF mode. I tried and it worked.

Now, all I am worried about is : Will pressing the DOF button while releasing the shutter cause any damage to the lens or body?

Thanks in advance for all your replies.