420ex flash

I have a g3 and a 420ex flash. When I take a photo inside with flash on of a person the flash only lights up the person and leaves the room dark but when I remove the person and take a photo of the same part of the room the whole room lights up. Why?

There are lots of reasons that this could be happening.

One reason,

You are setting flash lock exposure on the subject by pointing the AF point or box at the subject (person). Your flash is throttling back so as to not over expose the person.

Try bouncing the light of the ceiling. Youll find that the background will be better lit and the lighting on your subject will be more natural.

Are you shooting in auto, aV, TV??????, Can you post an example of the pic in question, it will be easier to assess what is happening.

Try "dragging" the shutter. This means using a slower shutter speed so that the details in the background can be captured too. This results in an image that has both well-lit subjects and background. The caveat is that you'll have to hold the camera steadier than before.

And if you have a typical subject, getting them to be still enough to eliminate blur will be a challenge. (Especially if its a natural shot, not posed).

Canon call this "slow-sync" (i've never heard of 'dragging' myself) and as you pointed out, gives best results if you use a tripod if at all possible due to the slower shutter speed.

j.