I'm looking for a cable release for a D2H, for long exposures on 'bulb', beyond the 30 sec. max shutter speed. What is the difference between the MC-20 and MC-30? About US$50 I guess, but is the MC-30 just as good for a manual release cable with lock on it? It appears the MC-20 has LCD panel with programmable timed exposures and MC-30 just has a manual-only lock and release w/o timer and display. Is this correct?