Re: PHOTO-3D digest 1366

[P3D Bob Howard <bobh@xxxxxxxxxxxxxxxxxxxx>]

RE: Flash sync bulbs and otherwise.

For those that may be getting confused. Electronic flash uses X-sync 
which means the flash is fired when the shutter if full open (for a 
focal plane this must be a speed when the first curtain opens the full 
width of the apeture, to be followed by second curtain. Higher speeds 
are a moving "slit" and this is what you will get a picture of the 
slit.)
Flash bulbs or the normal kind were M sycn. meaning they were fired 
about 20ms before the shutter opened and were at full brightness when 
the shutter did open. If electronic flash used on M setting it fires 
long before the shutter opens. Conversely, flashbulb fired on X sync 
will work IF the shutter speed is 1/25 or so as that is long enough to 
include the full burning of the flashbulb.
If the Realist was X-sync it would have to be used only at 1/25 with 
flashbulb.
It was my impression that early stereos were m-sycn only and had to be 
modified for electronic flash. MY Realist was modified so I don't know 
if it was once M.
The other class bulb was FP or focal plane with 20 ms delay and double 
peak (due to two cuts of aluminum foil) to last the travel time of a 
focal plane shutter slit. 
A Class F bulb with primer only gave a 1/200 sec. flash to stop action 
with box cameras etc. had 5ms delay so often used like X setting.
BobH


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