NASA Hasselblad EL data camera
Lunar NASA Hasselblad 500 HEDC (Hasselblad Electric Data Camera)
The same model as the one used to photograph the first steps of Man on the Moon (due to weight matters all HEDC used on the Moon were left behind with their lenses, only magazines were brought back to Earth. Hasselblad has offered to give a free magazine to anyone who would bring back one of their cameras from the Moon).
The HEDC is a Hasselblad HEC that NASA has been using since 1968 with two modifications, a new locking system for the magazine (the previous one was prone to involuntary opening). This is the reason why the HEDC models used for training were already equipped with this locking system but not the Reseau plate that required a longer preparation time.
The "Reseau plate" is an etched glass plate with 25 tiny crosses evenly set out to allow computing of distances on photographs.
Since this Reseau plate is mounted on the back of the camera, the Dark Slide cannot be used. That is the explanation for this notice : "Remove Dark Slide before installing magazine".
This Reseau plate system was used for the commercial model named MK 70 and used mainly for cartography.
