Telephoto lens help

I am a beginer in photography. I have just purchased a Minolta Dimage A200 and I baught a 3x telephoto lens, however, when I put it on it takes pictures that look like I am looking through a cylinder. I have changed the lens accessory setting to telephoto but it does not seem to change anything. any suggestions?
thanks

The 3x TC you are using is designed for much smaller lenses/sensors than the 2/3" sensor A200. There's nothing you can do about the vignetting, other than cropping the image later in editing.

The recommended TC for this model is Konica-Minolta's ACT-100 1.5x. If you want a higher power TC, make sure it's exit pupil (rearmost element) is close to the same diameter as the A200's lens.