Power isn't important, TTL isn't important, neither is brand. But I would appreciate at least three or four stops of adjustability. Is there a flash noticably smaller than, say, the Nikon SB-28, which fits the bill?
I know ND gels are a solution, but let's ignore that for now.
Nikon SB-27 allows 1/1, 1/2, 1/4, 1/8 and 1/16 power settings. It will also allow TTL, though I find the accuracy of the scale and manual settings quite good. Added nice items are the bounce card and macro reflector. You can also position the bounce card to act as a diffuser over the flash head to get a softer flash. This Speedlight packs into a slimmer and smaller area than an SB-28. I don't know if it is the smallest variable power flash, though probably the slimmest.
The Nikon SB-30 might be even smaller, though much more limited on settings. However, it might be just enough for what you want to accomplish. Both this one, and the SB-27 are common on the used market, and usually inexpensive.
Power isn't important, TTL isn't important, neither is brand. But I would appreciate at least three or four stops of adjustability. Is there a flash noticably smaller than, say, the Nikon SB-28, which fits the bill?
I know ND gels are a solution, but let's ignore that for now.
I'm not aware of any - most small flashes offer a choice of just one or two shooting apertures for a given film speed. Essentially, a flash needs to be quite big and powerful before it's worth providing a facility to go to 1/16 power (which is 4 stops of adjustability), otherwise this would be too weak to be usable.