Nice helmet of really good quality!
Here some info about the maker:
Yoshihisa (義久)
Myôchin Yoshihisa (明珍義久), late Edo period, lived in Mito (水戸) in
Hitachi province.
He was a student of the armorer Aizu-Myôchin Unai (右内) who was
hired by the Mito-daimyô Tokugawa Nariaki (徳川斉昭, 1800-1860) to
instruct the local armorers of the fief. In this sense Nariaki bestowed the
character for “Yoshi” (義) to the armorers and Yoshihisa was one of them. Hey
signed “Suifu-jû Myôchin Ki no Yoshihisa” (水府住明珍紀義久). Usually the
clan name “Ki” was only given to students of the Edo-Myôchin main line, but
Unai's master Muneyasu (宗保) also did not belong to the main line but as he
was an outstanding craftsman it is assumed that his use of the clan name Ki
was tolerated by the main line. Thus he probably also gave this name to his
own students.