On Tue, November 17, 2009 16:03, ADavidhazy wrote: > My students will be taking final exams tomorrow. You can review and > ponder about one of the questions (for entertainment value!) at the > following URL: http://people.rit.edu/andpph/a-pix/2009-sensi-1.jpg > > click! I wonder what I've overlooked or messed up? It's fun poking at these. The gradient suggests that the object was in horizontal motion during the period the shutter was open. Given the density at 1/1000 above, I'm going to treat the edge of detectable signal as the point where the edge of the object was when the shutter opened or closed (that's obviously not absolutely precise, but). The gradients on both sides also show that the object was in the frame at the start and end of the exposure; if it had moved through at a constant velocity starting after the shutter opened and finishing before it closed, there would have been a uniform streak of constant density. The area of uniform density in the middle of the bottom photo shows that the object was in those areas for the same amount of time. Thus, that defines the area that the object moved through during the exposure. You don't actually say that the bottom photo was shot at f/8, but I think it has to be for us to do much with this problem, so I'm going to assume that. The density of 1.25 shows that the object was in that area for very close to 1/30 sec (that gave 1.3). The object was thus moving at a rate of (width of constant area in second photo) per 1/30 seconds. -- David Dyer-Bennet, dd-b@xxxxxxxx; http://dd-b.net/ Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/ Photos: http://dd-b.net/photography/gallery/ Dragaera: http://dragaera.info
