I bought a cheap page magnifier for the purpose of putting it on my GG.
In the meantime however, I've been playing with it; holding it up to a wall opposite a bright light and observing its imaging abilities.
The image it creates is wonky to say the least, but it's also quite interesting. It is also very bright!
I'm wondering a couple things. First, what would the f/ stop be? Finding the focal length would be simple enough, but how much of the diamater should I consider as lending to the maximum aperture, if that makes sense.
The other thing is whether or not creating a simple aperture/mask will increase the quality of the image. I'll experiment with this when I get home and see what the result is.
At any rate, if you've got a fresnel lens, take it out and play with it. It might have some potential for interesting images.
Anyone ever done this?