What are you referring to as digital zoom? The t3i has no digital zoom that I am aware of. Remember digital zoom is just cropping, you can do that in post. If you are referring to zooming in while doing a live view shoot, yes you can do that, but it's not a zoom, the image will not be 'zoomed in' when shot. That is a feature for checking focus. For example, if you are shooting a portrait you might zoom in to the leading eye of the subject, and manually focus to make that leading eye razor sharp, producing a desirable focus results perhaps more accurately than a T3i can provide automatically. When you take the image though, it'll be of the entire subject, not just the eye.