[pure-silver] Re: [SPAM] Re: correction for bellows extension
- From: `Richard Knoppow <dickburk@xxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Wed, 04 Mar 2015 23:13:13 -0800
On 3/4/2015 10:04 PM, mark@xxxxxxxxxxxxxxxxxx wrote:
Ok Houston, I now have a problem. When using a studio flash, what I
set for a shutter speed matters little. The duration of the flash is
only going to be so long, and the flash is done long before the
fastest shutter speed on my shutter can close. I think its 400th of a
second, and most SLR's and DSLR's have a sync speed of 1/250th. With
natural light, the sun last all day, but not so a flash. When most of
the light comes from a flash, and what is in the room that doesn't
either is likely overpowered or is an accent in the image, time is set
for you.
Still if you double the amount of time, or open the aperture one stop,
you still allow the same amount of light to hit the film. Now each
will affect the image differently, but the same amount of light gets
to the film. By a factor of three I take that to mean three times the
time. That would mean three times the light.
I can turn up the lights maybe to three times their intensity, but it
would not be hard to need far more power than I have available to make
that happen. Maybe practical for many, but I probably would run into
limits quickly.
That leave f stop, and to get three times the light to the film, that
is a stop and a half by opening the lens and allowing more light in.
I am sure I am missing something, but why wouldn't this work.
Still as one said, open one stop at 11in and another at 16in, and its
probably good enough have a negative that is easily printable as long
as the initial exposure was good to begin with. Still one thing I
learned in digital is the closer you get to start with, the less time
and the easier it is to deal with later.
Why does everything seem to be so complicated??? lol Oh well guess
that's part of the fun too.
I'm not sure I understand this correctly. If you are using strobe
flash you can not vary the shutter speed since, as you say, the duration
of the flash is usually shorter than the fastest shutter speed.
However, for fixed subjects you can use multiple flashes. However, the
film does not usually record them linearly due to reciprocity failure.
That is, two bursts may not add up to double the exposure. It depends
on the film and the intensity of the light at the film. Changing the
aperture works regardless of the shutter speed. The correction factor
must be translated from the linear factor to the square law calculation
for the stop. You can think of this as the hole being further from the
film so it looks smaller to the film. Its opened up so it looks the
same size. The aperture is the only choice you have for strobe unless
the strobes are adjustable for intensity or duration time at the same
intensity. In some set-ups you can move the lights closer to increase
the intensity (works for either flash or hot lights). I have come to
the conclusion after very nearly three-quarters of a century, that
_nothing_ in life is simple.
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
WB6KBL
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