# The Dictionary Of Photography

### A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

 Instantaneous Photography To find the distance moved by the image of an object on the ground-glass, multiply the focus of the lens in inches by the distance in inches moved by the object in one second, and divide the result by the distance of the object in inches. Example. - Find the displacement of image on ground-glass of an object moving 20 miles an hour, with a lens offocus, and the object 150 yds. distant. per sec. practically. To find how quickly a shutter must act to take an object in motion, that there may be a circle of confusion less than i-iooth inch in diameter, divide the distance of the object by 100 times the focus of the lens, and divide the rapidity of motion of object in inches per second by the result, when you have the longest duration of exposure in fraction of a second. All measurements in inches. Example. - Required the speed of a shutter to take an object moving 20 miles per hour, with a lens of focus, the object being 150 yards distant. Knowing the rapidity of shutter and moving object, required to find the distance to place the camera to give an image with a circle of confusion less than of an inch in diameter. Multiply 100 times the focus of the lens in inches by the space through which the object would pass during the exposure, and the result is the nearest distance in inches between object and camera. Example - A shutter works afsec, object moves four miles an hour; how near must camera be placed with anlens ? An object moving four miles per hour moves 72 in. per second. 404