Here is an article explaining how to do it.
Desktop video magnifiers are one of the great assistive technology solutions for those with a vision impairment. The price for these devices can be cost prohibitive in that they usually start at upwards of $2000. The iPad has opened the door for many individuals to have a powerful magnifying device that is also portable. This is going to show you how to turn the iPad into a desktop video magnifier by constructing a simple stand and connecting the iPad to a TV for under $90.