Doremus - if I'm not completely mistaken, I think there's a complete difference between most if not all 35mm camera focal plane shutters and large format - at least based on my single sample MPP press which I assume to be a common design.Originally Posted by Doremus Scudder
The 35mm SLRs usually have two blades, both of which move from the same edge but with one some time later than the other: the first one opens and then the second follows it, giving either a moving slit of a specific width for faster speeds, or a fully open gate for slower speeds. The thinner the slot, the less time that a particular point on the negative is exposed, even though the blades move at much slower speeds.
The large format camera I have, and a number of elderly medium format cameras (I no longer have) had a roller shutter which has a number of slots of varying width cut in a single blind. Once again the width of the slot gives the exposure for a single point on the film, but not all points are exposed at the same time. As the blind is wound to a desired speed, I'd assume that the spring tension increases for faster speeds, and that the slots are not therefore necessarily linearly related to exposure time.
To measure an exposure time for *any* type of shutter, the easiest way - if you can drive an oscilloscope - requires only a fast light sensor and the oscilloscope. An LED will generate a voltage output (at very low current) when exposed to light: green ones give most in daylight. Connect the led to the input of the scope, place it at the point you want to measure (the centre is a good place to start) and point the lens at some light. Sticking the LED through a black card will keep light from the back of the camera.
Neil
Reply With Quote
Bookmarks