Some basic things you need to know about Canon flash...
If you have the camera set to any of the auto exposure modes (Av, Tv, P, for example) and the flash set to ETTL, the camera will set exposure according to the ambient light (hence the really slow shutter speed you're getting) and treat the flash as "fill", approx. 1-2/3 stops reduced power.
If you instead set the camera to M or "manual", it will then treat the flashy as "full", as if it were the only light source. And, so long as the flash is set to ETTL mode, it will still give you "auto exposure". The flash will fire more full powered typically
(In either case, you can vary the power of the flash a bit by dialing in some + or - Flash Exposure Compensaion or FEC. This is just like dialing in Exposure Comensation when not using flash. Neither FEC or EC are possible in the highly automated exposure modes: the "Scene Modes" or "full auto" such as "A+" or "the Green Box".)
However, you are further complicating things by "trying to take a closeup". Depending upon just how close you are, it might be too close for the flash. I don't know about the T3's (or any other) built in flash, but flashes made especialy for macro work are fairly low powered. The MR-14EX has a guide number of 14 and the MT-24EX has a guide number of 24. In comparison, a 580EX II that I use has a guide number of about 198. I do some macro flash work with over-powered flashes, though, by diffusing the flash. I just put several layers of white gauze over the flash tube, to reduce the flash's output. If your flash is over-powering the images, you might need to do something similar.
I also don't know about the built-in flashes (because I never use them), but the accessory flashes display a distance scale on their LCD screen, based upon the camera and flash settings. This is a big help when shooting flash images and trying to judge if you are too close or too far away (and would need to change your camera or flash settings to compensate).
Also, shooting really close, the built-in flash might not be usable because it is partially blocked by they lens or the flash is pointed "above" the subject.
But, give it a try. Set your camera to M, choose a shutter speed at the flash sync speed (1/200) or slower, choose your aperture and set the flash to ETTL. For closeup shots, you'll probably want a middle to smaller aperture to have enough depth of field. You can vary the shutter speed slower or faster (up to 1/200) to render more or less of the ambient light, along with the flash light. And you can vary the ISO as needed to get into the power range of the flash (unless you are so close that even with the lowest ISO the flash is still overpowering the image, in which case you'd need to diffuse the flash).
As the previous response suggests, there is probalby a setting where you can enable or disable Auto Flash. I think there also is a "Flash On" scene mode. I'd never use these and don't have a T3, so you'll need to check your camera's menu or consult the camera manual.
Hope this helps!
***********
Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & EXPOSUREMANAGER
