Hi, total newb here. I've been experimenting with live view for the last couple of days but if I try to zoom in in live view everything goes blurry and out of focus, sorry if this is a stupid question but I just can't figure it out!
For a lens to remain in focus whilst zooming it has to be of a special design known as Parfocal, obviously it costs more to make lens like this so most cheaper zoom lenses don't incorporate this facility and will need refocusing as you zoom. Providing you achieve initial focus at the long end of the zoom you can usually get away with it for video use especially if you use a small aperture to get a large depth of field, for still photography where you may be seeking a higher definition or are using a large aperture then it is best to refocus.
It is not possible to use optical zoom in live view mode as the camera is using its sensor to create the live image, and the lens is not actually moving. When you zoom in, the camera is digitally zooming the image which can cause it to become pixelated or blurry. To use optical zoom, you will need to switch to the camera's regular shooting mode, and use the zoom ring on your lens to adjust the focal length. Once you have set your desired focal length, you can switch back to live view mode to compose and focus your shot. Keep in mind that zooming in can affect the depth of field and potentially make it more difficult to achieve sharp focus, so you may need to adjust your aperture and shutter speed accordingly.
I think your confusing the OP, the DSLR can zoom in on preview image in live view. To the OP...... The DSLR is not actually zooming the lens or actual image because there is no optical or mechanical zoom of the lens on a DSLR. It would be done by hand.