Try this incredible soft of drawing painting! http://www.madewithmischief.com/
There is a free version!
With six essential brushes, a basic palette of colors and an infinite canvas, Mischief-Free is perfect for hashing out ideas, life drawing, and endless doodles!

What do you think of the zoom 50 * "10 power 18" for 1 !
And the infinite canvas and infinite resolution ?