Extension rings are required if the minimum focal distance of a lens needs to
be reduced. They are available in a range of thicknesses and can be combined
to produce almost any desired extension. The usefulness of a set of extension
rings cannot be overstated, as they allow the parameters of almost any lens to
be simply and easily altered.
Pentax Ricoh extension rings are suitable for all C-mount and cs-mount lenses
from Pentax Ricoh, Tamron and many other manufacturers.