If you've made it out with your cameras, lenses, and tripods for the predawn, doesn't make any sense at all not to wait for dawn.  Photographically to me, dawn is that time of the day immediately before and just after the sun comes up over the horizon.  The image used as a title banner on this page is what I would consider dawn -- the sun has already broken over the horizon, you just don't know it yet since it is still hidden behind the rock formation that the Nubble light sits atop.  These images were all taken from quite a distance on the road that runs along the beach in York with very long telephoto lenses - focal lengths ranged from 300 to 900 mm. 

CAUTION: never look through a long telephoto into the rising or setting sun.  Doing so can cause permanent and irrepairable damage to the retina and even blindness!!!