Magnifiers

The simplest magnifier is your smartphone. The main advantage is ... you always have your smartphone with you.

Search for a magnifier application. Try one that can use the LED on the back of your smartphone as well. The application may have a negative function (that could show white text on black background from a black text on white paper) - or you could configure a shortcut to switch the whole phone to negative mode from the accesibility section in settings menu.