Re: Enablement - Flash terms

[Godfrey DiGiorgi]

GN == Guide Number ... A number that allows you to calculate the 
correct aperture for proper exposure using flash at a given distance 
and ISO sensitivity. For instance, if a flash has a GN (in feet) of 50 
with ISO 200 film, it has the full power enabling you to set f/5.6 for 
photographing groups at 8-9' distance.

GN is often used as a power rating, usually quoted at ISO 100 in feet 
and meters.
---

P-TTL == Preflash-Through The Lens flash metering ... TTL flash 
metering says that there is a sensor which watches the film/sensor 
plane *during* the actual exposure and sends a signal to a compatible 
flash unit when enough light has reached the sensor to quench the 
output. P-TTL goes beyond that: it makes a flash prior to the actual 
exposure and combines the ambient TTL metering with the flash to arrive 
at the proper exposure, then makes the actual flash and exposure 
afterwards.

Godfrey
On Mar 8, 2005, at 5:12 PM, Shel Belinkoff wrote:
What does "GN" mean?  The swivel head and being able to make bursts 
sounds
like neat features.

Shel

[Original Message]
From: Sylwester Pietrzyk

Higher GN (40 at 50mm/iso100 vs. 30 in Pentax), swivel head (AF360 has
only
tilt movement), "Multi-Pulse Flash Function" - burst of low power 
flashes
that enables you to catch subject's movement steps on one frame.