I did this to measure the shutter speed of my LF copal shutters. It worked very well and has been useful a number of times. While the lens is in spec, I measured almost a half stop error at the fastest shutter speeds. It also showed that they become more repeatable after 3 or 4 practice exposures. Such is life with old mechanical devices. the tricky part was to set the trigger on the o-scope and determining the area under the curve as this is the only way to measure all of the light. Andy On Jan 28, 2011, at 12:15 PM, Christopher Strevens <chris@xxxxxxxxxxxxxxxxx> wrote: > I think the photodiode and oscilloscope a really good suggestion. Or a > counter-timer and photocell to measure the duration of light. Safer than > guns! > > Chris > > -----Original Message----- > From: owner-photoforum@xxxxxxxxxxxxxxxxxx > [mailto:owner-photoforum@xxxxxxxxxxxxxxxxxx] On Behalf Of David Dyer-Bennet > Sent: 28 January 2011 16:49 > To: List for Photo/Imaging Educators - Professionals - Students > Subject: RE: flash duration > > > On Fri, January 28, 2011 05:00, Christopher Strevens wrote: >> Flash duration is about 1/10000 sec. I would think a bullet from a gun >> that >> has just been fired. Use a wire to hold the flash off so it triggers as >> the >> bullet breaks the wire. The circuit would be a transistor going to ON to >> fire the flash and an transistor I the inverting amplifier configuration >> holding the flash fire transistor off until the wire is cut. >> >> The muzzle velocity of you gun should be available from the gun smith and >> so >> the length of the blur will enable you to compute the duration of the >> flash. >> >> Warning! Guns are dangerous so don't shoot yourself or anyone else during >> the measurement. You will need a couple of sandbags to safely stop the >> round. > > Using an air gun is somewhat easier, in that you don't need as heavy a > backstop, and the legal complications aren't as messy. > > With a real gun, the muzzle velocity varies with both the gun itself, AND > the ammunition. However, if you know anybody who reload seriously, they > probably have a chronograph to measure how their ammunition is performing, > so you could use that to get a fairly accurate reading on the bullet > velocity, and then in turn use that for measuring your flash duration. > > At this point, however, it might be easier to find somebody with an > oscilloscope instead, hook up a photocell and power source to it, and just > expose the photocell to the flash. > > -- > 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 >
