RX100 with close up filter

sem wrote:

The sensor is not an issue here, the short zoom is. Weak diopters magnify enough when used on a 300mm lens (and do it at a very long working distance). Weaker achromats are useful on bridge cams with long zoom (and wide-enough aperture there, otherwise diffraction softens images).

The Raynoxes are good for the money I believe, and probably the right diameter too. You can also use a reversed short prime if you've got one lying around, 50mm is +20 diopters - but attaching heavy lenses is also an issue.