fill flash vs non-fill flash questions.

When I'm in a studio, using monolights, flash controls the exposure, and for
the most part, shutter speed is irrelevant, this is my understanding, which
is confirmed when I use a flash meter which does not give a shutter speed,
only an aperture reading, so shutter speed must, I can conclude, be
irrelevant in this type of flash photography.


But when I'm outdoors, using a dedicated flash unit, such as my Autoflash
SunPak 433 TTL, in fairly bright light, I'm using fill flash to add light
to shadows, and in this situation,
as I understand it, flash is not controlling exposure, but ambient light
is, is that correct? Am I correct to assume that fill flash intensity is
less than EV (ambient) light?


If the above is true, then what EV threshold is it that TTL flash will
switch from a fill flash mode, to one similar to the studio set up wherein
flash dominates the exposure, and shutter speed only controls the ambient
(background) exposure?

Or, does one have to switch manually, or does this happen automatically at a
certain EV threshold in some flash units, or does the camera determine this?


By the way, on my Oly, I'm using a FL-40, on my Elan IIe, I'm using an auto
433AF thyristor.


Best,

Patrick

 

From: "Patrick L."

Yes, so long as the ambient light is dim enough.

Yes, if the flash is set lower than the ambient, but if you have the flash
setting too high it can overpower the ambient.

It is if you set it correctly, but you can set the flash separately to be more
or less than ambient. Obviously if flash is the fill light it needs to be less
than the ambient.

If your studio setup has the fill light ratioed 1:3 to the main then for a
similar fill ratio you'd meter the ambient (which is now the main light) and
set the flash for a 1:3 fill ratio.

For your Elan IIe, I'd suggest one of the Canon EX speedlights. Then fill
flash is a snap ... just use AV mode and set the flash to E-TTL (it will then
make all the measurements to balance the flash with the ambient). If you want
the flash used as fill light you'd set the flash to underexpose. You need to
experiment to find the exact values to use but with my EOS-3 and 550EX flash I
get excellent fill light in AV mode at either -1 or -1 1/3 stops flash
compensation. Much less and the flash is just a catchlight, much more and the
flash is too noticeable.

Dunno what you'd use with the Sunpak since it's not an E-TTL flash, but those
numbers should be a good starting point.

Bill

 

?

Okay, in situation where the sun is key, and flash is fill:

I can meter the flash with my flash meter, and I don't have to set a shutter
value on the meter, but if the key light is the sun, and, say I'm using
ASA 400 film,
I can take an incident reading, but how do I compare to the flash reading to
the incident reading, when the incident reading requires a shutter speed
value and the flash reading does not? (On the incident reading,
reciprocity shift changes both aperture and shutter values, inversely, so
how do I know if I"m at 1:3, when the key light is the sun, and the fill is
flash?) The only value for comparison is the aperture reading for the
output flash, and ? what from the key light (ambient) reading? Do I
use the incident aperture reading with a shutter speed set to at a standard
1/125?

Patrick

 

From: "Patrick L."

Ah, you have a flash meter ... this makes it easy

The shutter speed doesn't matter for the flash, so long as the shutter speed is
set for the camera's max sync speed (maybe 1/180th or 1/125th on your Elan?) or
slower. So just use the aperture reading to set the flash power.

Pretty much ... just set the camera with the proper aperture/shutter speed for
the ambient (key), making sure the shutter speed is slow enough to sync with
flash, then meter the flash and reduce the power on it in manual mode until the
flash aperture reading is high enough for the fill you want. So for example if
the ambient aperture setting is f/11 then move the flash (or change the power
setting) until you get a reading of f/8 with the flash meter for a 1:2 ratio
(shooting at f/11 means the flash will be underexposed one stop since it needed
f/8 to be correctly exposed). Two stops (ie, flash aperture reading of f/5.6)
means a 1:4 ratio, etc. Test bracket between 1, 1.3, 1.6 and 2 stops to cover
the range from 1:2 to 1:4 ratio to see what looks best to you.

As you move closer or further from the subject the flash will need to be
recalculated if metering by hand, which is why I recommended the EX series of
Canon flashes, since this recalculation is done automagically for you without
having to use an external flash meter. Since you said your flash has TTL
metering you might be able to mimic this by setting the flash compensation to
underexpose, if the flash offers that option.

BIll

 

Due to the short duration of electronic flash (my Metz manual says about
1/7000 of a second) shutter speed is pretty much not an issue with flash,
just aperture.
Think of it this way:
If you were in a dark room with no ambient light at all and your flash said
you could get f 11 at 10 ft @ ISO 100 then as long as you had your shutter
at a speed that would sync with the flash (usually 1/125 or under, depending
on your camera) you could shoot any speed you wanted as long as you were at
f 11. Any speed from 1 min(for example) to 1/125 of a second would give you
the exact same exposure.
I don't know the specifics of your camera, so I will explain manual fill
flash going back to the example you gave of a person outdoors. If their
face was partially in the sun and you had an incident reading of f16 at
1/125th of a second @ISO 100 you would set your camera to that and you would
set your flash to give you f11. This will give you that 3:1 ratio, main to
fill.
No matter what your ambient exposure in this example your flash is putting
out f11.
Now using the law of reciprocity you could shoot the same scene at f22
@1/60th of a second and if you didn't change the power on your flash or move
closer you would still be getting f11 out of your flash, giving you a 5:1
ratio (I think), or hardly any fill value at all.
So you can see why there is always choices to make in selecting your shutter
speed and aperture, even on a bright sunny day and especially if you are
trying to use fill flash.