Bill D. Casselberry said:
Gregory L. Hansen wrote:
... And I've had it up to here [insert proper gesture] with
estimating distances and calculating apertures because
I'm pushing it past the thyristor specs.
Years ago I made up a plain gridsheet in ExCel and entered
the figures from the onboard slide-calculator gizmo from
whatever flash I had then. It's all straight inverse square
stuff, so you can just enter extrapolations from the patterns.
Ran it from 25asa out to 3200asa - I vaguely remember about
300ft for 3200asa @ f1.4 (or something far like that) for
a 4-AAcell unit, ~ GN80
I printed it out and maybe it'll surface. Probably still
somewhere on the drives also, I suppose.
Estimating distance is annoying. And using up rolls of film to find
actual guide numbers to use for my shooting situations is annoying. The
nominal guide number is for a small room with brightly colored walls;
much of the light is reflected from the walls and ceiling. Outside you
should cut the nominal guide number by about a half. I suppose that
depends on the divergence of the beam, but just divide by two in a pinch.
I haven't tried snow, I'd guess 3/4 and bracket.
But once I have an effective guide number, the calculation is probably
faster to do in my head than to pull out a chart and look it up. It's
g=fr, guide number goes as the square root of energy, so it's just linear
in aperture and range. And for nominal g0 at 100 ASA it will be
g=g0*sqrt(film speed/100 ASA) because required light is linear
in film speed. So with 1600 speed multiply by 4, much easier than trying
to extrapolate it from those calculator slides that have positions for 400
and 1000 (who ever heard of 1000 ASA, anyway?).
I spent an evening once working this out, and figuring out how to
calculate the combined effects of multiple flashes at different ranges,
and flash with significant ambient light. So I know how to do, for
instance, a main flash and fill flash even with two manual flashes with
the same guide number, by adjusting the ranges. And that's fine when I
have time to meticulously plan a photo, but really sucks for spontaneity.
