It may seems obvious, but the "proof is in the picutre".
Thanks, Chuck, for emphasizing my point. All the technical analysis
DOES have a use, i.e., to help us understand how to use the equipment.
But it is, afterall, only equipment, in pursuit of a picture that
communicates. Richard and Graham's images come to mind. Not to exclude
=anyone else= on the list, of course.
Earl
Chuck Norcutt wrote:
>Relative to my flash coverage measurments, Andrew asked:
>
>What were you using for a target and how far away was it?
> - If it's too shiny instead of matte, light will bounce away
> from the lens instead of scattering in all directions
> - If it's too close even a matte surface will have falloff
> as it won't be perfectly "lambertian".
>
>Earl also responded with:
>Since there is no universally accpeted standard for the term "coverage"
>or "covers", in this context, it really depends on the specific photo's
>requirements.
>------------------------------------------------
>
>There was no target. What I listed are direct, incident light
>measurements using a Sekonic L-358 flash/light meter at a distance of 10
>feet from the flash head. The 10 foot distance is to an imaginary plane
>(wall) directly in front of the camera. Obviously, some (if not all) of
>the falloff is due to the fact that all of the measurements except the
>center are actually somewhat further away than 10 feet. How much is
>reflector/flash tube design and how much is the inverse square law I
>don't know. I haven't done the trig and am not so inclined.
>
>This is probably a good illustration of Earl's point. Do we really
>expect "coverage" to provide even illumination over the imaginary wall
>or do we accept that this is a very tough requirement given the inverse
>square law. Should I have measured falloff from the center of an
>imaginary sphere 20 feet in diamter such that all measurement points are
>precisely the same 10 feet from the flash?
>
>While there are certainly no standards, I opt for measurement across the
>flat plane. Using that as a "standard", what I have pointed out is that
>the two competitive flashes I measured provided equal or better evenness
>of illumination at a coverage angle wider than their stated
>specification than the T-32 did at its specification. Thefore my
>statment that Oly is optimistic.
>
>I reiterate that no actual film was exposed to injury by high speed
>photons during any of these experments. YMMV.
>
>Chuck Norcutt
>
>
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