[rollei_list] Re: Flashbulbs

----- Original Message ----- 
From: "John Jensen" <jwjensen356@xxxxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Tuesday, May 31, 2005 4:02 PM
Subject: [rollei_list] Re: Flashbulbs


> To clarify the designations of F and SM, I went to the
> flashbulb site I spotted a couple of days ago:
>
> "Type SM "Class F". - These GE Speed Midget Class F
> (fast peak) flash bulbs were designed for use with
> focal plane shutters, usually at 1/60 second shutter
> speed and stopped action like a strobe flash. Bayonet
> Base. These bulbs reached their peak of use during the
> early 1960s.  Gas filled. "
>
> It looks like the purpose of the SM bulbs is to
> provide quick action with focal plane shutters at the
> slow speed when the curtain is entirely open.  I
> presume the FP bulbs have the long duration for use
> with the focal plane shutter at hegher shutter speeds.
>
> John
>
  See my post. Class F or Speed Midget bulbs were not 
intended specifically for 35mm cameras. They _could_ be used 
with them at a slow enough shutter speed so that the entire 
aperature was open at some point, just like strobe. The main 
purpose, as I pointed out, was for use on cheap cameras with 
simple shutters. The Speed Midget, because of its nearly 
intantaneous ignition did not need a delay mechanism at 
relatively slow shutter speeds. Box cameras and other cheap 
cameras seldom have shutter speeds of more than 1/50th 
second. This is enough for a SM bulb to come up to full 
intensity while the shutter is still open when the bulb is 
triggered simutaneously with the shutter by a simple 
contact. Actually, Class-M bulbs can also be used with 
shutters that have no delay provided that the shutter speed 
is slow enough so that the shutter doesn't close before the 
lamp has come up to full intensity. For practical purposes 
that is around 1/25th second. In normal use the shutter 
speed controlled exposure over a fairly wide range just as 
it does for steady light. Because the gas filled SM lamp had 
such a short dwell time, perhaps 1/200th, the lamp dwell 
controlled the exposure time, again in a manner similar to 
strobe.
   Since the Class FP bulb for focal plane shutters had 
sufficent dwell time the FP shutter could be used normally, 
as it can't with strobe. A FP shutter set at 1/1000th second 
has greater motion stopping ability than a Class-F Speed 
Midget lamp. A Speed Graphic equippled with a multiple 
reflector flash gun and using its focal plane shutter was a 
common tool for certain kinds of sports photography, 
particularly boxing where the photographer was generally 
close to the boxers.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 

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