canon G3 and Philips flash-synch problem

"Yves Kropman" <y.kropman.TakeThisOut@betuwe.net> wrote in message
news:1069258253.772334@rh9cache...
 > Hi,
 > I have a new digital Canon G3 and a very old Philips flash P356 CL-X. The
 > flash works fine, but is there a way I can use it with the Canon? It
fires
 > at full power, and trial-and-error does not bring me good pic's.
 > Suggestions? Thanks, Yves.
 >
 >
Do you have any documentation on the Philips Flash?
The information that you need is the Guide Number (GN) at what ISO (ASA).

If you had a Flash Meter, you could just meter the flash and set your camera
to the reading on the Flash meter.

For correct exposure with a flash:
Exposure is determined by aperture, subject distance from flash and ISO.

The shutter speed does not affect the exposure, except for ambient light.
In the case of a focal plane shutter, the shutter speed must be set at a
speed that the shutter if fully open during the flash fire. That does not
apply for a digital camera (no focal plane shutter).

The formula is f-stop = Guide Number divided by Distance in Feet.

f-stop = GN/Distance

The Guide number is only correct at the ISO number that you measured the
distance.

Guide Numbers can be in Feet or Meters, If the Guide Number is in Meters,
then the distance must be measured in Meters.

For trial and error set the distance to a fixed target. Put the G3 camera on
Manual:
Set aperture to f8 and the shutter speed to 1/125. Set the ISO to 50. Flash
set to External.

Make a series of test shots of the target by moving the camera (actually the
flash, the camera can stay in the same spot) a measured distance from the
target.

Look for a correctly exposed image.

Example: Measure the distance with a tape measure. (Don't guess!).
Place the camera (with Philips flash) 10(ten) feet from the target, take a
shot with the above manual setting.

If the image is under exposed (dark), then move to 7 feet. Shoot, if still
under exposed, move to 5 feet. 3.5 ft. is next. If you are under exposed at
5 feet, throw the flash away. The flash is not usable, it is too weak.

If the image is overexposed (too light, the whites are burned out), then
move the flash to 14 feet from the target. Check image. If still over
exposed, make another shot at 20 feet. If still over exposed move to 28
feet.

A one stop change of exposure is made by moving the square root of 2 times
the original distance. (1.414 times 10 ft = 14 ft for the first one stop
change).

After you find the distance that you get a correct exposure, then the Guide
Number of the flash is:

f-stop times Distance in ft. = Guide Number in Ft.
f-stop * Distance = GN

In your case, you are using f8, so.

8 times Distance in ft. = Guide Number at ISO 50.

8 * Distance = GN

To convert the Guide Number for different ISO numbers:
For ISO 50 no conversion ( You tested at ISO 50)
For ISO 100 Multiply the Guide Number by 1.4
For ISO 200 Multiply the Guide Number by 2.0
For ISO 400 Multiply the Guide Number by 2.8

My Sunpak Auto Thyristor 522 has a GN of 120 at ISO 100 which is GN 86 at
ISO 50.
For ISO 50, f8 the distance would be 86/8= 10.75 ft
For ISO 100, f8 the distance would be 120/8=15 ft. For my Olympus C2040Z
this is the closest at full power. ( I don't use full power).

That is the closest this Sunpak flash can be to the subject on full power
with today's digital cameras without a Neutral Density filter.

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