A method is provided for manufacturing a three dimensional frame structure that can be used as a core structure in a sandwich construction. In order to extend the expectation of serviceable life of the connection, the pipe nipple of the reservoir used as a collector or distributor is made of a nickel-base alloy and directly welded to the collector wall in such a manner that an axial gap remains between the connecting branch and the collector wall. The method also comprises redistributing respective bit sequences of at least portions of the first image and the second image by respective amounts arranged to effect the reduction of the phase difference between the first image and the second image. The enclosure member has a lip that opens to allow the tip to move forward and extend from the writing instrument so that writing fluid can be delivered to the writing surface for writing. An optical path incident on the first reflecting surface 22 and an optical path exiting from the second reflecting surface 23 intersect each other.