Nikon

MC-DC1 is the shutter cable used for Nikon DSLR, such as D70, D70s, D80

Because the shutter for DSLR is control by digital signal and not by mechanical means, so it is different from the shutter cable used for mechanical camera such as FM, F2, FM2.

Extracted from Nikon webpage.
See http://www.nikon.com.hk/productitem.php?pid=847-0170126fed
MC-DC1為四針之遙遠控制接線，用於遙遠控制快門釋放按鈕。當要避免因相機震動而影響拍攝時，就能使用這條遙控接線控制快門。