In article <a05001901b8d6ea27a86b@[165.247.214.9]>,
Stephen Scharf <scharfsj@xxxxxxxxxxxxx> wrote:
> Ian,
> Thanks for the info....I'll look into this, but I'm still a little
> confused....I've never used a flash unit before, so I am still a
> newbie when it comes the guide numbers thing and all....what is the
> flashmatic system? The auto mode seems to have two f stops, F/4 and
> F/8 available on my T20. Which one do I use? Do I set the camera for
> say, 1/60th of a second?
Guide numbers... ok then. The flash guide number gives you a simple
relationship between flash-subject distance and aperture. It will be
quoted as <number> in <feet or meters> for <film speed>, e.g. 20 (meters,
ISO 100) for your T20.
The guide number is the aperture you would need to set for the quoted film
speed if your flash-subject distance was 1 distance unit.
So, using the example of your T20 again, for a subject 1 meter away, using
ISO 100 film, you'd set an aperture of f/20 (22 would be close enough).
For other distances, divide the guide number by the flash-subject
distance. For a subject 2m away, that's f/10 (11 is close enough).
For other film speeds, multiply the guide number by <film speed used/film
speed given by flash guide number>. So, using our T20 example again, for
ISO 400 film, multiply by 4, for ISO 50, multiply by 0.5.
The flashmatic system is Olympus's name for the mechanism built into their
rangefinders which automatically sets the correct aperture for the
distance the lens is focused at. Obviously, you have to set the correct
guide number for your flash and film.
The T20's auto mode uses a sensor on the front of the flash to pick up
light reflected from the subject when the flash fires, and shuts off the
flash when it thinks enough light has been cast on the scene. It assumes
you have set the aperture on your lens to the setting on the flash.
If you're using an OM body, shutter speed should be 1/60 or less.
Rangefinders with leaf shutters (like the 35RD and Canonet) can be used at
any of the available speeds.
hth
--
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| / | |/-\ | Ian A. Nichols |
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| * i.a.nichols@xxxxxxxxxx |
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