So i read that on some dslr's, by leaviing the shutter open for say, forty five minutes, can overheat the sensor. I have a nikon d200. My question is, how long can i safely leave the sensor open. Or, should i just set it up with automatic exposure at 5 second intervals, with a 30 second exposure each for a total of the forty five minutes?? What is the best idea? Also, as a side note, i want to be able to take the longer exposures of lighting so i can get multiple ones on one exposure. If i get the cord where i can lock the shutter open, how long can i expose it safely. So basically, how long can i leave the shutter open without overheating it, And if i set it at 30 second exposures, how long should i leave inbetween for cooling?!!??! Thanks in advance!!