Re: Could someone please explain this? Class FP flash bulbs are intended for Focal Plane
shutters. The bulb is designed so that the flash duration is
extended for long enough, and the output over that time
uniform enough, for use with focal plane shutters provided
the shutter is operating within certain limits. Most Class
FP bulbs require the same delay as a Class M bulb; 20
milliseconds. Because the total travel time for the shutter
on a miniature camera is fairly short FP bulbs offer the use
of flash over most of the shutter's speed range (varies with
the camera). Since all flash bulbs require some time to come
up to full brightness synchronizers fire them before the
shutter is tripped.
Class X synch is for strobe flash. The flash is triggered
when the shutter just reaches fully open. For a focal plane
shutter the speeds are limited to those where the shutter
aperture exposes the entire frame. For older 35mm cameras
this is typically 1/60th second. At higher speeds the
shutter exposes only a slit of varying width so only a part
of the frame will be exposed by the strobe.
When bulb synch is used with a strobe the flash is set
off well before the shutter opens regardless of the shutter
speed. When strobe synch is used with bulbs the bulb will be
fired late so there will be reduced or no exposure depending
on shutter speed unless a very slow speed is used.
FWIW, there are several classes of flash synch:
Class F (Fast), 5 milliseconds (miniature and gass filled
bulbs). These could be used in simple cameras with long
shutter speeds and simple, non-delayed synch.
Class M (Medium), 20 milliseconds (most older bulbs)
Class FP (Focal Plane), 20 millisecond delay but long
duration for focal plane shutters
Class S (Slow), more than 20 millisecond delay. These were
very large bulbs meant to be used open flash (wihtout a
synchronizer) in studio reflectors.
--
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com
There are also other bulb types, flash cubes, etc.
Richard Knoppow
|
|
