----- Original Message ----- From: "Uptown Gallery" <[email protected]>
> This may be off topic, but the breadth of knowledge within this group may > provide me an answer (off list , if necessary). > > I would like to understand (actually, analyze) the operation of a focal > plane shutter, for the purpose of building one for sheet film. I want to get > a grasp on calculating exposure duration as a function of slit width and > linear speed, I guess (or direction to what I should be thinking about). Let me thin in "written voice" here: Since the film will be stationary, if we draw a very thin line on the film (parallel to the shutter's slit), when the slit is moving accross the film it will see that thin line passing by, the amount of time it takes that line to go from one end of the slit to the other will be the exposure time. Exposure time, therefore should be given by: Exposure time = slit width / speed of shutter moving across the film for instance: If you want an exposure time of 1/60 seconds and you have a slit 2mm wide, you FP shutter should move this fast accross the film: FP shutter speed = Slit width / Exposure time FP shutter speed = 2 / (1/60) = 120 mm/second If the film is 4x5 (landscape), the FP shutter should take this long to move accross the 5" length of the film: Time to move accross film: (5 x 24.5) / 120 = 1.0208333 seconds Thinking over !! Guillermo
