The H 20 camera back mounted on Hasselblad 503 CW with Winder CW seems to lock the camera body, which creates difficulties in making an exposure.
Even though the H 20 camera back acts as a full-fledged part after being integrated with the camera house, Phase One does not recommend the H 20 camera back to be mounted on Hasselblad 503 CW with Winder CW. In case you have mounted the H 20 camera back on Hasselblad 503 CW, you will have to acquire a special motor cable 50300119 (Motor Cable for Phase One H 20 for Hasselblad 503CW can be supplied by Phase One). This cable is set between the M-connector on the H 20 and the DIN connector on the Hasselblad camera body. The motor cable ensures the two-way electronic communication between the digital back and camera, providing an opportunity to shoot from the shutter release button on the camera or capture from the computer.