The lower image is a blurred image of a square object. It is blurred because the object was in motion. The white object moves three inches. This is determined by comparing the length of the second image with the side-by-side images above it. The squares have a space between them so as a ruler they are actually slightly more than one inch each, but I've chosen to ignore that for this exercise. The object is moving at a constant rate. This is determined by observing the even brightness of the image. The dark ends are the result of the amount of time the subject is "in front of" that piece of film. In the center of the image the subject is in front of a given point for the amount of time it takes an object to move one inch when traveling at 170.45 MPH. Since the object moves three inches in this exposure and the object one inch wide it is in front of a point in the center for 1/3000 second. We can not tell if the object was moving left-to-right or right-to left. At the beginning of the exposure the object was at one of the edges. At the leading edge, the object had left that point in almost zero time during the exposure, That is why the exposure is dark there. At the trailing edge the object is just arriving at the end of the exposure. Again there is almost zero time for exposure there. In the center of the image there is a two inch segment where the exposure is constant. any given point in that segment was illuminated by the object for 1/3000 second. To the right an left of that segment any given point is illuminated for a lesser time. The moving object has a reflection density of 1.25. This is between the values for the exposures of 1/15 and 1/30 of a second. That means the moving subject was "over" a point in the center of the image for between 1/15 and 1/30 of a second. Therefore it was moving between 15 and 30 inches per second. The exposure was between 1/5 and 1/10 of a second. Either that, or the object is moving at nearly the speed of light. It is glowing white hot at a brightness not normally observed on earth. And time dilation has spread it out over a short distance. The shutter speed must be nearly instantaneous for all practical purposes. Either way is fine with me. Tim On Tue, 2009-11-17 at 20:29 -0500, ADavidhazy wrote: > Chris, > > Interesting take on this. Not quite hat I was expecting. Need to think about it. > Anyone have insightful comments on this? A couple of observations ... regardless > of how big the image of the "target" is it is given that the subject is 1 inch > or 25.4 mm so size on screen does not matter. > > I don't quite understand: "In the second photograph the subject is a vertical > black object and the background is lit". - Hmmm are "we" thinking in negative or > positive terms? Interesting. A possibly ponderable alternative. Hmmmm ... but it > seems the original premise was turned around as it is given that the background > was NOT lit - it was a very black background. So some thought has to go into this. > > have fun! > andy > > > Chris wrote: > > In the second photograph the subject is a vertical black object and the > > background is lit. The object is oscillating from side to side and completed > > one cycle during the exposure. > > > > The sides of the second print are black because the object is stationary > > briefly there and the gradation is due to its acceleration in Simple > > Harmonic Motion as the object spends less time obscuring the light as it > > speeds up. > > > > In the middle the object is travelling at its maximum speed and at a density > > of 1.25 (given above) the exposure time is 1/20 second. The object travels > > about 1 cm on my screen print size and so is doing 1 cm in 1/20 second so > > about 20 cm/sec. > > > > > > Chris > > > > > > -----Original Message----- > > From: owner-photoforum@xxxxxxxxxxxxxxxxxx > > [mailto:owner-photoforum@xxxxxxxxxxxxxxxxxx] On Behalf Of ADavidhazy > > Sent: 17 November 2009 22:04 > > To: List for Photo/Imaging Educators - Professionals - Students > > Subject: Sample question FYI > > > > 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! > > andy > > >
