The projector is very simple. It's made of cardboard, duct-tape, and a Fresnel lens about 7"-10". I found that using a Laptop works the best, because the screen is larger to begin with, and it can be turned up fairly brightly. This is good because as the image is made bigger, the intensity of the light on the screen is lessened. An image of 50" is very watchable on a Laptop, as well as a Tablet about the size of an iPad. Of course, the closer your bring the projector to the screen, the smaller the image will be, but the brighter and more focused it will become. I found that if you cover all your windows and close any doors to make sure the room is completely dark, this will help the image appear crisper and brighter.
Because the Fresnel lens is made flat, there are some optical disadvantages that appear in the image. For example, the edges of the screen may be a little blurry while the center is in focus. To address this problem, a shroud can be added to the lens with a rectangular hole in the center about the size of a credit card. This will choke down the aperture, and dramatically improve the focus. The trade off is that there will be less light emitted from the projector, so the image on the screen will be dimmed. A Smartphone works the same way, but the screen size can't go much over 20" or the image is unwatchable. 15" worked great, and 20" was ok. Some Smartphones don't have an option to lock the screen sideways so you may have to download an app for that.