This one is for the resident mad scientists. I think the MagFilter is a pretty neat concept. Being more interested in other filters, though, I'd like to hear about methods other people have used to attach filters to the front of compact camera (or other smooth, unthreaded) lens tubes. In particular, methods that allow for reasonably easy on/off, and don't compromise the pocketability of the camera or filters. I'll eventually get around to posting the method I've used in the past (it's hard to describe without images), but I'm hoping to collect some other, possibly better, ideas here.
I literally just hold up the filter to the lens and take the picture. I'm too cheap to buy multiple sets of filters for both my DSLR and compact cameras, so I buy one larger set for the DSLR lenses and use that all the way around. I've done the same thing with my smartphone and my DSLR filters too.
I've had attachments that slip-fit over a smooth outside cylinder. Especially in a compact camera, the base of the lens is a plain cylinder that is wider than the extended lens.
I saw some dyi ringflash plans that used a split piece of pvc pipe, where the original pipe was a bit smaller than the lens barrel to slip over. Opened to fit around the lens, it makes a C shape, and two were glued together to make a pvc ring of the desired size from a pipe of a different size.
You can fasten a base to the tripod mount that extends in front of the camera, and mount other things on that. If "close up filter" you mean a macro lens (basically a magnifying glass) you need to keep it lined up, not twisted, and in justnthe right spot. The rail where the magnifier can be slid back and forth is a conventional approach.
For less than full aperture, you could take a lens cap (it holds on to the end somehow, right?) And cut out the middle.