Actually a periscope is an optical device made with mirrors, it is listed with the nondigital vision devices. As such it should not be able to take any digital enhancements just like the optical binoculars built for mages. Smartlink, lowlight, thermographic, and image enhancements should not be installed on a device that has no capacity.
EDIT: Sorry, it turns out there are actually two periscope items. I saw the one in optical devices. The one as a gun mount should due fine treated as capacity 3.