Sorry, sent accidentally. It's unfinished and needs mods and another
experiment.
Chuck Norcutt
On 7/14/2014 8:35 PM, Chuck Norcutt wrote:
After all that toil and trouble over getting an auto flash unit to
operate correctly with an ND3 filter I decided to revisit auto flash for
daylight fill flash. I know I've done it successfully in the past and
(by poor memory) thought I was simply lying to the flash about the ISO
setting on the camera. Not so.
I first started by examining all the documentation I have on my various
old auto flash units. I have 4 T-32s, a Sunpak 422, a Sunpak 522
(potato masher type), a Minolta Auto 360 PX and a Vivitar 550FD. None
of these user manuals discuss doing daylight fill flash in other than
manual mode. I even checked some manuals for flash units that I don't
own (such as the revered Vivitar 285HV). Much to my surprise no mention
there either. They all say to use manual mode flash.
So then I started looking to see if I could find instructions for
daylight fill flash using flash controlled auto mode on the web. It
took a fair amount of digging but I finally found it... on Ken
Rockwell's site <www.kenrockwell.com/tech/fill-flash.htm> where he
predictably sings the praises of using Nikon gear in Program mode but
later on gets to older cameras and recommends using auto mode for
daylight fill flash. His simple prescription is set the camera for the
ambient exposure, then set the flash for the same ISO and set the flash
for one stop down or a wider aperture than being used on the camera.
eg: If the camera is set for an ambient exposure at ISO 200 and f/8
then set the flash for ISO 200 and f/5.6. He never questions whether
this is actually possible. But Ken Rockwell is a Nikon man so I suspect
the the 1980s Nikon flash units have the necessary auto modes and 1 stop
spacing to make this work. I've never owned a Nikon flash so don't know.
But can actually deal with these specific setting on a T-32. If you set
the ISO slider at 200 the three auto mode aperture settings available
are f/5.6, f/8 and f/11. But these three apertures are your only
possible settings. Trying to shift the aperture range unavoidably
changes the ISO as well.
It gets even more restrictive using other than the T-32. Except for the
Sunpak 522 all of the others have their auto mode ranges 2 stops apart.
So trying to use these for fill flash in auto mode makes the fill
light at least 2 stops down vs. the more conventional 1 stop down. The
Sunpak 522 is the major exception here. It not only has 1 stop
increments but provides 4 auto mode ranges vs 2 or 3.
Next, how does auto mode actually work? Durned if I know. One thing
that we do know is that the flash fires all at once. Flash power can't
really be modulated. The only thing you can do is control the amount of
time the flash is allowed to drain from its capacitor. If the flash at
full power drains the capacitor in 50 milliseconds if it's set at 1/2
power it will only be allowed to run for 25 milliseconds.
So, how well does it actually work? So, so. I set up my flash meter at
ISO 200, set the flash at ISO 200 and then tried triggering the flash in
each of the 3 auto mode ranges; f/5.6, f/8 and f/11. The flash meter
actually measured f/3.6, f/5.0 and f/7.1. All are below their nominal
value by 1-1/3 stops. How come? I don't know. I considered that this
is an old flash and maybe a bit weak. But then again I tried all of the
other (admittedly old) flash units and found them all wanting on the low
side. In defense of the flash units though I should point out that if
it measure f/5.0 from 10 feet it also measured f/5.0 from 16 feet. One
would like both consistency and accuracy from one's flash unit but
consistency is more important... the rest can be calibrated.
One major possibility for the error in output has to do with the flash
unit's measurement of exposure. The Sekonic light meter is measuring
incident light from the flash and I believer these numbers are correct.
The flash doing the controlling, however, is working on reflected
light from the room where the testing is being done. Ideally I should
have a big medium gray backdrop to reflect the light but I don't have
one big enough.
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/
|