Fernando, good to see you're getting out there and giving it a go. You won't learn how to improve your shots sitting inside at home. Firstly, two and a half minutes on a fairly bright globular cluster like 47 Tuc is probably overkill, even at 400 iso. You've done well to keep the stars round at such a long unguided sub but the core is blown out too much. Being out of focus doesn't help either. My suggestion would be to reduce your exposure to about 1min, or better still, do a series of subs with varying exposure times and stack them together in a program such as Deep Sky Stacker. That way you'll help retain detail in the core with the shorter subs and capture the fainter outer stars with your longer ( 2min ) subs. Make sure you focus carefully though as this won't improve your result if your focus is out. Try focusing using the highest magnification on your camera's Liveview function and lock the focus on your telescope to prevent it from moving. Good luck!
