An exact answer to the question "how long" is not possible, since the waves come in a varying speeds, and you have to experiment. I have a set of ND filters from 3 stops to a Big Stopper (a 10 stop!) that I fiddle with on a Nikon DSLR. A polarizer will account for 1 to 2 stops at its maximum setting. Please look at the photos at this gallery, all on a tripod with DSLR, all by me:
SD Coastline | robertrose.photos
These were all at dawn or dusk, on a tripod, and with boots on to slog through water and over rocks. The exposure was generally f/16 and around 2 seconds.
For this to work you must turn off auto ISO, and auto exposure, or the camera will try to compensate for the darker scene by upping the ISO or opening the aperture. On a DSLR this works best on the M mode.
Yes, it is possible to get a wave movement by taking a burst of stills with a drone, and then stacking them in Photoshop. If you do that, you probably will want to edit out all but one of the "non-moving" areas so that (rocks for example) part is sharp. That is a lot of time sitting in front a computer, however. If there is no wind, then I suppose that a single 2 second exposure with a Phantom is possible. I have not tried it, but you should investigate the "tripod" mode:
"In Tripod Mode, the maximum flight speed is limited to 5.6 mph (9 kph) and the braking distance is reduced to 6.6 ft (2 m). Responsiveness to stick movements is also reduced for smoother more controlled movements. Only use Tripod Mode where the GPS signal is strong or light conditions are ideal for the vision system. If GPS signal is lost and the vision system cannot function, it will automatically switch to Atti mode. In this case, flight speed will increase and the aircraft cannot hover in place. Use Tripod Mode carefully."
P4P User Manual, p. 26.
One of San Diego gallery was selected by judges to appear in the San Diego County Fair last summer:
Windansea 2 | robertrose.photos
To the comments that criticize the photo that tml4191 posted, let me respond that I know of no photographer who is trying to maximize verisimilitude, e.g., merely recording the scene as exact as possible. I know that I am not. I am trying to show you something you haven't seen before, and do so in a way that conveys some emotion. Even when I make a commercial photo for a realtor, I don't want to have it show the house "as it really is" but rather "as it could be." Maybe I get you angry. Maybe I make you contemplative. Maybe I make you happy. Maybe I make you relax. In any of those cases I have succeeded. Further, when photographing for myself it is not enough to just record a photo with studium (e.g., that which is typical of photos of that genre). I try for elusive punctum (e.g., that which pricks, such as the people on the cliff here
Sunset Cliffs 2 | robertrose.photos), or the water appearing to flow out of the rocks here
La Jolla | robertrose.photos)
Thanks for reading through to the end. Ramble over.
Bob Rose
www.barkingdeerphotography.com
www.robertrose.photos
www.rosepatents.com