[MrB (Simon)]

Originally Posted by Benny L

from memory you can get adaptors that have a filter thread on one side and a lens mount on the other allowing you to reverse mount lenses.

Novoflex does one for canon eos:

http://www.novoflex.com/en/products/...ter-eos-retro/

There are also filter-filter adapters for mounting two nifty50's objective-objective.