If you happen to purchase one of the Franiec lens rings for the Canon G9, (shown here- it's all back vs. the Canon's stock ring which has a silver stripe around it), be aware that there's a slight trick to getting them on properly.
The ring must be mounted with the small bayonet flange facing up. Be gentle, and let it click into place. If it's forced on, the only way to remove it is to cut it off. This seems to be a common problem, as we've seen many of these that have been forced on.