Magic Filter Extender???

[Arvee]

I picked this up at the thrift store in a box with some filters and haven't a clue to its function. It is a 52mm filter extender(?) that is 11.11mm thick that has a male 52 thread on one side and a female 52 thread on the other side. The only markings on it are "X52 Germany." I can't imagine why one would want to extend a filter 11.11mm(vignetting) so it obviously has some other purpose. Ideas, anyone?

 

[Dr Croubie]

Complete guess, but if you used a diopter / close-up lens, would increasing the distance twixt it and the lens make the picture better?
Otherwise I can't think of any reason to vignette on purpose, unless it's for long lenses doubling as a hood?

 

[Newt_on_Swings]

Sometimes there are lenses that have front elements that push out a bit and if you were to screw on a thick filter it would contact the lens. This gives that lens a bit of space. Some people even make these by breaking a filter and removing the glass to get a male to female thread of the same size. They are sold now cheaply on ebay, but a little while back they were not as common.

 

[Arvee]

After a bit of research, it could be an adapter for coupling telescopes/binoculars to Nikon 52mm camera lenses.