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Re: [OM] To OM or not to OM

Subject: Re: [OM] To OM or not to OM
From: Richard Schaetzl <Richard.Schaetzl@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 17 Jun 1999 16:46:39 +0200
KenK1ZYW@xxxxxxx wrote:
> 
>> So, assuming I want to do fill flash at a 1:3 ration of this subject wearing
>> a wide brim hat at high noon using ISO 100 film with my Zuiko 100/2.8, how do
>> I set my OM4T and F280?

> Yes Warren, this is my point. The Oly flash system is great except for this
> major flaw. Contemporary flashes allow this calculation easily -
> automatically. 

Do they? Really?

How would they calculate an exact 1:3 ratio? 

Flashes are point light sources. The flash ilumination of an object is
depending on the distance to the flash. Natural light from the sky is an
uniform light source, equal ilumination for objects in all distances.

For fill-in, how do the camera know how far away your object is?

Nearly all (save P&S) automatic fill-in flash systems measure the
intensivity of both, flash and natural light. Even N*k*ns so called "3D"
metering is reling primarly on measuring the intensivity of light,
distance information is used best as an "limiter" preventing
overflashing. For measuring the distance, information of an wide angle
are not very usefull, you can not measure the distances of far away
objects.
And what happens to objects closer to the flash than your main object,
overflashing? Or do you have to skip your 1:3 ratio for your main
object, reducing flash output even more in the interest of an balanced
exposure?

As long as the light intensivity is measured, keeping an exact 1:3 ratio
(or any ratio) is not possibile (and maybe not desirable).

> I had a situation photographing the most incredable birds in Florida at Weeki
> Wacchi where a blue heron in full "landing configuration" and heavily backit
> was photographed and was a great picture except for the need for a little
> fill flash to bring out detail and perhaps get some specularity - so a good
> shot was not the great shot due to flash equipment issues

Are there flashes available, which have enough power, to fill-in flash
an object, say 20m away?

> If the F280 can do this type of exposure, it should have been documented
> somewhere.

And the N70? How far away was the bird? If it was as far away as I
think, you would have had no chance for controlled fill-in anyway,
regardless of the flash you used.

But maybe you could have used an Metz CT60 + teleconverter, GN(metric)
60x1.7=102. 
Then you need an camera which can sync at 1/250s, AFAIK the N70 can´t,
but anyway 1/250s is an tad slow to use with an 300mm lens. 300mm are
the minimum you have to use with birds, I think. 
The rule of 16 states an exposure, for ASA100, of 1/60s at f/16 or
1/250s at f/8. 
The range of the biggest portable flash know to me, the CT60 plus
converter, with this aperture, is 102/8=12,75m.
So every object at an distance farawaier than 12.75m will get an fill-in
ratio just depending on this distance.

BTW the flashes recomended by the camera manufactors for fill-in (their
own) have much lower GNs, 50 for lenses longer 100mm, that´s an distance
of 6.25m at f/8.

> Maybe it is documented and none of us know about it?  (Hummm I don't think so)

Maybe, but maybe we should also check the advertising promises of camera
manufactors for their plausibility?

Regards

Richard


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