These were made with the Polaroid back for an RB67 converted to a pinhole camera, on expired Polaroid 669. I made two versions of this camera, one with about 2 inches of focus, the other with a flat piece of card stock right over the P-adapter, giving a focus distance of only 14mm! That one has some serious falloff. :)
The sunburst is just that - point the pinhole right at the sun for a couple seconds and that's what you get.