From: "P. J. Alling"
On 3/14/2012 8:32 AM, John Sessoms wrote:
From: "John Coyle"
I started with blue flash-bulbs in 1967. They had a long burn time
(1/40 to 1/60 second)
with a rapid climb to full output, then an even peak output followed
by rapid drop-off at
the end of the burn. The 'M' setting on the camera I was using at
the time (a Voigtlander
Vito CD) was what you used for these bulbs, although the camera also
had an 'X' setting
for them new-fangled electronic flashes.
The settings ensured that the shutter opened first, then the flash
fired. The shutter
speed had to be set at 1/30 or slower, so that the flash output
occurred while the shutter
was fully open, otherwise you'd get a black bar at one side or the
other, where the film
was unexposed. Aperture was calculated from the guide number of the
flash and the speed
of the film, and I found I could seldom close down beyond f8, even at
400 ASA. The bulbs
were coated with a blue substance to match the colour temperature of
noon daylight, so
fill-in flash was possible.
There was a third shutter setting option, FP ('flash-peak'), which
would allow the use of
bulbs designed for focal-plane shutters, and these you could use at
speeds from 1/30th
upwards to 1/1000th, although I never had a camera with that facility
until I got a
Rolleicord, where you could use the 'V' setting to fire the flash at
any speed - basically
because the shutter was a between-lens type.
Open to correction on some of the technicalities, it's been a long
time since I had to
think about such matters!
I think the M-sync fired the bulb first and then opened the shutter.
FP sync did that, the standard luminance chart for FP bulbs shows a
sharp spike which then trails off at a relatively constant light out put
for quite some time afterwords, I tried to find an image of that chart
but couldn't. Just imagine a chart of these arbitrary numbers
Flash fires --> 0 1 15 20 15 14 14 14 14 13 13 13 12 11 9 7 5 3 1 0
The shutter opens when the value drops to 15 to insure that the film is
relatively evenly exposed. That's what FP bulbs were all about.
M sync the shutter begins to open then the flash fires (on a leaf
shutter before the shutter is fully open, but on a focal plane shutter
after the shutter is fully open to capture as much of the light as
possible.
The chart for M bulbs is more like this
Flash fires -> 0 1 15 20 15 10 5 3 2 1
http://camerapedia.wikia.com/wiki/Flash_sync
Some older cameras support M sync, which supports flash sync with (now
obsolete) medium-speed electric flash bulbs. Because flash bulbs take
some time to generate their maximum light output, M-sync is timed to
fire the flash slightly earlier, then opening the shutter so as to
coincide with that peak output.
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