Hot answers tagged shutter-speed
Put it in Manual (M) mode and roll the wheel until it shows 'Bulb' on the display. One shutter button press opens the shutter, another closes. You don't need a remote, but it helps to prevent camera shake to a great extent. P.S. The manual is your friend.
At 1/250, you are trying to exceed the x-sync speed of the 6D (which is 1/180, as you have found), which explains the black bar. Don't forget that on the 450D, as a crop-sensor camera, the shutter has less distance to travel, so doesn't need to move as fast to give the same exposure time, which explains why some full frame cameras have a slower x-sync speed ...
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