[rollei_list] Re: Rolleiflash Disaster
- From: aghalide@xxxxxxx
- To: rollei_list@xxxxxxxxxxxxx
- Date: Tue, 08 Dec 2009 00:49:21 +0000
Harold Edgerton used flash to produce a stroboscopic effect. He was famous for his high-speed stop action photos. The high-speed photography was instantaneous. Flash bulbs are not instantaneous. They require what was called m or f synchronization. Camera shutters used to offer either x for instantaneous for electronic flash, or m or f delay which represented the time between when the shutter was fired and when the flash went off. You have the possibility of 3 delays for the flash when you click the shutter on older cameras. Only x has been retained, and they don't even call it x.
Ed Farber brought the electronic flash to the populace. He used a 510V battery to obtain enough voltage to produce the flash. The studio units utilizing low voltage battery packs were often very large and heavy and not practical. Eventually with the advent of the transistor to produce enought voltage the units were smaller and more practical. In some cases too small. He invented a high speed electronic flash in a company called Strobo Research in Rochester, NY. Which was bought by Graflex and permitted him to retire at an early age. rather than use a very large electronic flash to produce high speed result, Ed Farber (I edited his column about flash) used what I think was a rectifier to take the low voltage from the batteries and make it a high voltage. These rectifiers were very large. With the advent of the transister in 1959, Multiblitz in Germany did away with the rectifier and used transisters to increase the voltage from the battery pack to produce a practical hand-held electronic flash unit.
Ed Meyers
-------------- Original message from "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>: --------------
>
> ----- Original Message -----
> From: "Don Williams"
> To:
> Sent: Sunday, December 06, 2009 3:34 PM
> Subject: [rollei_list] Re: Rolleiflash Disaster
>
>
> > At 04:34 PM 12/6/2009, Jim Brick wrote, in part:
> >>On the day of the wedding, as we all emerged from our
> >>rooms at the
> >>Inn, Mark tested the lenses that he was going to use for
> >>photographing
> >>the wedding. Hasselblad, 50mm & 80mm lenses. He took the
> >>film back off
> >>and fired the camera while looking at the flash, through
> >>the camera
> >>from the back. On the 80mm lens, he either wasn't seeing
> >>the flash
> >>(strobe) or was seeing the shape of the diaphragm.
> >>Clearly, his 80mm
> >>lens was not working with flash.
> >
> > I learned this trick the hard way. For graduation from
> > High School I got an Argus C-4 which served me until I got
> > in the navy. During my midshipman cruise I picked up a
> > battery-powered strobe (67.5 volt battery I believe) in
> > Panama.
> >
> > I tried to take pictures with the new strobe and the C-4
> > but they were always under exposed, whether using the M or
> > F sync setting, and even when I kept using larger and
> > larger lens openings.
> >
> > I finally shot the flash at the back of the lens with the
> > back cover off and saw that the limiting factor was the
> > behind-the-lens shutter, which was acting as an F-stop
> > with the strobe. I eventually ground a new cam section on
> > the shutter driver to get a true X sync, which I connected
> > to the M socket.
> >
> > The C-4 was a nice camera for me at the time but it had a
> > tendency to break the shutter toggle bar and I finally
> > retired it, around 1953 when I got my 2.8C. I kept the
> > Argus until a year or so ago when I gave it to some
> > collector, knowing that it had a broken toggle bar.
> >
> > You can learn a lot about sync by looking at the back of
> > the lens assembly using a strobe for illumination.
> >
> > DAW
> >
> This is a good test for strobe (X) synch. If you have a
> 35mm camera where the back is accessible you can also
> determine the highest speed at which the focal plane shutter
> can be used for strobe. Up to some speed the entire negative
> area is exposed at once. At higher speeds the slit is
> narrowed and only a portion of the negative will be exposed.
> FWIW, Class-M synch, which is appropriate for a great
> many flash bulbs is defined as 20 milliseconds, that is, the
> flash lamp takes about 20ms to come up to full intensity
> after it is energized. The shutter is usually set to be wide
> open at this point but some shutters use slightly more or
> less delay so that the peak of the lamp falls into the open
> time of the shutter. Unlike srtobe flash, where shutter
> speed makes little or no difference to exposure the dwell
> time of a flash bulb is comparable to medium shutter speeds
> so the exposure will vary with the shutter speed. This is
> reflected in the guide numbers given for the lamps.
> Two other classes of lamps may be encountered: Class S,
> for slow, and Class-F, for fast. The latter are gas filled
> lamps with a 5ms delay between energizing and peak output.
> Some cameras have a setting for this but Class-F lamps were
> meant mainly for use on box cameras and other simple cameras
> with a simple contact flash tripper and slow shutter speeds.
> When used on a camera with a slow shutter speed, say slower
> than 1/50th the shutter time will be long enough to
> accomodate the flash even though there is no delay. Class-S
> lamps were meant to be used with open flash, i.e., one opens
> the shutter and fires the lamp. They have a delay of around
> 50 ms. Most of these are very large lamps meant to be used
> in standard studio reflectors to illuminate large areas.
> They were also used for early color films which were very
> slow.
> There is an additional type of bulb, the Class FP,
> these are meant for use with focal plane shutters. They have
> about a 20ms delay but the dwell time is long enough for the
> small shutters in 35mm cameras or for a Speed Graphic
> shutter when used at its highest speed. In 35mm cameras the
> travel time of the shutter is usually constant, the speeds
> being controlled by the size of the slit. In the S.G. and
> similar cameras, there is a choice of both slit size
> (several different sized slits in the same curtain) and
> travel time. The "tension" adjustment regulates the travel
> time. Certain Class-FP lamps have just enough dwell time to
> work with a 4x5 or smaller S.G.
>
> --
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
> ---
> Rollei List
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