I got a Canon EOS Rebel T3i last June. It was a big step up from my three previous Canon point-and-shoot digital cameras. I want to take pictures of basketball games. I decided that I need two camera bodies so that I can equip one with a zoom lens for closeups and one with another lens. I bought a the newer model, the Rebel T4i, which uses the newer DIGIC 5 processor rather than DIGIC 4. It can shoot 5 frames per second rather than 3.7. When it arrived last Friday, I went to a local basketball game and came home disappointed. My new camera, when equipped with my fastest lens (50mm/f1.8 ) took fairly pedestrian images. After, I spent a day going through my 317 images and cutting them down to 24 decent ones, I tested my camera against my old one. I performed two tests. I put the fastest lens on each and took a picture of my bedroom wall with automatic mode. The T3i shot at 400 ISO, while the T4i shot at 1600 ISO. Then I took my 18-55mm kit lens and set it at 50mm (f5.6 max). Again 400/1600. I think this means that my new camera is not properly calculating its parameters correctly. I sent it back in to Canon yesterday. I am hoping Canon will fix this.
I'm a nikon user so I'm not familiar with the specifics of the two bodies mentioned but the newer one should out perform the older one in low light conditions. Your t4i may be using a higher iso because it has better high iso performance. I know my older nikon looks about the same at 400 as a newer one does at 1600. So your camera may just be using a shorter shutter speed or narrower aperture mixed with a higher iso.
To know if there is actually a problem with the camera body you'd have to compare the shutter speed, aperture and iso used for images taken with both cameras.
To do best in low light situations without flash I'd recommend shooting in either full manual or shutter speed priority. Set your aperture as low as it will go (f/1.8 in this case), change iso auto to 400-800 then see what kind of shutter speeds your able to get. If you shoot in full manual you can go with shorter exposures that under expose the image and brighten them up during post processing with software (shooting raw images is best for this).
The main advantage of a dslr vs a point and shoot is that you are able to manually change the settings!
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