How to use lens filters on RICOH GR series

A separate adapter is required to use a lens filter with the RICOH GR series.
The usable adapters differ depending on the GR series version, so please see below.

GRⅢ

RICOH genuine lens adapter [GA-1]
https://ricohimagingstore.com/lensadapter-ga-1-s0037817.html
It is possible to attach a wide conversion lens GW-4 with a magnification of 0.75x and a φ49mm filter.

GRⅢx

RICOH genuine Lens adapter [GA-2]
https://ricohimagingstore.com/lensadapter-ga-2-s0037826.html
It is possible to attach the teleconversion lens GT-2, which allows shooting at 75mm equivalent (35mm format conversion), and a φ49mm filter.

GRⅡ

RICOH genuine Hood & adapter [GH-3]
https://www.ricoh-imaging.co.jp/japan/dc/option/lens/
A set that includes a hood and an adapter for attaching a φ49mm general-purpose filter, etc.

GR DIGITAL III / DIGITAL IV

RICOH genuine Hood & adapter [GH-2]
https://www.ricoh-imaging.co.jp/japan/dc/option/lens/
This is a set that includes a hood and an adapter for attaching a φ43mm general-purpose filter, etc.

GR DIGITAL II / GR DIGITAL

RICOH genuine Hood & adapter [GH-1]
https://www.ricoh-imaging.co.jp/japan/dc/option/lens/
A set that includes a hood and an adapter for attaching a φ37mm general-purpose filter, etc.

Please see the RICOH homepage for details.