vertigo wrote:
I once had a salesman's calling card which was the size and thickness of a credit card but was a plastic fresnel lens__wow, look, it magnifies! Mounted it on the front of a bellows on my 35mm and managed to get a more than recognizable image. Certainly not "tack sharp." But fun and interesting none the less. Bellows from a broken Poloroid camera ($1 at a garage sale) glued to a body cap with a large hole drilled through it.
The 5 inch glass fresnel lens can be gotten from any electrical contractor supply store, sold as replacements for damaged or broken covers for over head recessed pool lights that are used around the pool in exterior buildings. They are super cheap, especially if you have a contractor's number (Texas it is called a tax number), from fifty cents to a few dollars each.