It's difficult to say any number of dives in order to say you should take a camera...
As many have stated, you are pretty much a solo diver at the time you take a camera. The better prepared you are for diving, the better prepared you will be when you take a camera.
There is always a risk when you take a camera. That risk is greatly increased when you are new to diving, uncomfortable with new equipment or... even diving a new site. I often leave my camera on the boat when diving a new site. I much prefer to get the layout and feel for the dive site. I can always come back and dive it again with a camera (possibly not, if I had the camera and ran into trouble on that first dive).
Before taking a camera into the water, I first ask myself if I am comfortable with my equipment and the environment. If the answer to this is no... the camera stays (sometimes I stay with it... lol)
The second thing I ask myself is if I am comfortable with my buddy's skills? If the answer is no... the camera stays (I would prefer to be there for the buddy if I am not comfortable with their skill set)
The third thing I ask myself is if a problem arises, am I prepared to ditch the camera in order to survive (can be a question with the cost of cameras, housings, flashes and lenses). I am willing to ditch it at any time someone's life may be on the line (But, I ask myself this question every time I dive with my camera anyway)
The last thing I ask myself is if I am physically able to make the dive with a camera and make all the skill moves needed to protect the reef, wreck or structure I am diving. You must be prepared (trained, practiced and skilled) in order to make some of the moves that will put you in awkward positions to get the shot, protect the environment and get yourself back out of whatever you get into (a hole, upside down, back fin... etc) These skills take time, practice and ability to keep the dive site in the same (or better) condition as it was when you hit the water...
Does this all mean you should not take a camera at your skill level? I don't know about you... You must answer this.
Was I prepared at your skill level? NO!
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As some have stated, learn your camera inside out on land, get your buoyancy under control, then take it on some shallow dives where risk is minimized. Get comfortable with diving, then... get comfortable with underwater photography!