Bulb ramping is a technique to record the transitions from light to dark or dark to light. Basically using the bulb mode of the camera and the controller will ramp the exposure time according to how the light is changing. In other words you are changing the exposure over time in EV by adjusting the time in bulb mode. Aperture is constant. There are a couple of controllers that do this quite well, the Promote Controller and the Little Bramper. This is used during timelapses mostly. The ramp is user adjustable and basically you need to watch the histogram on the incoming images, after you have done it a couple of times you get a feel for it and it is not that hard to do. Here is a timelapse I did to learn how to do it, it goes from full day to night back to day with a smooth exposure transition:
Alan
edit for P.S. the lights you see flashing around after dark are red flashlights, this was taken at my observatory, which is the roof you see off the right.
