Eyes, then Binoculars: Unless you found a bird or other object of interest by scanning with your binoculars, you will want to quickly and fluidly go from naked eye to a magnified view. The best way to do this is keep your eyes on the bird. Then simply raise your bins to your eyes, and voila, the bird is there, especially if you remembered to. . .
Pre-focus: Often, you have a sense of how far away the next binocular target will be. Prepare for it by pre-focusing at that distance – point blank for butterflying, out at the limits for raptors. When in doubt, set the focus wheel at a middle distance.
Pete Dunne and Michael O’Brien scan the skies from the dike.
Raptor Scanning Fundamentals: Pre-focus your binoculars on a cloud or airplane to get the distance right. Face the direction you expect the birds to come from (north, generally, in the fall). Scan left to right or right to left along the horizon, with the horizon just visible in the bottom of your field of view. Raise your binoculars one field (the amount you can view at one time through them), and scan back again. Repeat until you are looking straight up. Scan relatively slowly, since it is easy to pass a high-flying bird without seeing it, and think “small” and “distant.” Pause for a minute or two after each scanning sequence to rest your eyes, and also to scan without binoculars to catch that Merlin blowing by at close range.
Binoculars for Twilight Viewing: I’m still pretty sure the brightest binocular in the world was the old Zeiss classic 7 X 42, but any quality binocular 8.5X or less and with an objective lens of 40mm or more will be great for dawn and dusk. Avoid 10X binoculars and stay away from compact binoculars for this use.