Here's a copy of something I sent to Phil a couple months ago when he
asked for some help in doing manual fill flash. First, there's an error
where I said the sync speed of a 5D is 1/250. It's only 1/200. I've
never tried it but, for fill flash only, I suspect you could actually
get away with cheating on the sync speed a bit as Phil suggests.
I also have an example like Phil's using the sun as a hair light and
fill flash for the shadows. <http://www.chucknorcutt.com/personals02.php>
The fill flash here was similar to this T-32 rig but on a light stand
instead of a tripod and triggered by radio slave. You can join the two
T-32's with a short TTL cable and attach the receiver to the PC/hot shoe
adapter as seen on the left side flash unit.
<http://www.chucknorcutt.com/gear/Umbrella%20adapter%20mounted%20on%20tripod%20%232.jpg>
OK, on to manual fill flash. I should also add that my examples show
one stop less than the main exposure but you might sometimes want to be
down a bit more than that like 1-1/2 stops. With digital you can also
do as Phil suggests and just start at some distance and 1/2 power and
chimp and adjust until it looks right. Your best and easiest fill shots
will be with the subject and background in full shade with the possible
exception of some grazing sun for hairlight as above. Next comes full
sun. Mixed sun and shade is to be avoided if at all possible since that
is not a fill flash situation.
Dr. Flash
=================================================================
First let's review non-fill flash where the flash is the main light. If
you don't have a meter you need to use the flash's guide number. Let's
work with a T-32 with a full power guide number of 104 feet at ISO 100
or 1/4 power guide number of 52 feet at ISO 100. (are you UK guys still
familiar with feet?) Divide the guide number by the distance from the
subject to get the aperture. If you're 10 feet from the subject you get
104/10 = f/10.4. On the 5D with 1/3 stop increments you could choose
either f/10 of f/11.
Since all flash manufacturers tend to lie a bit about the guide number
of their flash units I'd be inclined to round down to f/10. Actually,
I'm inclined to round down a lot more than that since exhaustive flash
meter testing of all four of my T-32's shows that the actual guide
number for a T-32 with fresh alkaline batteries is 84 instead of 104 and
with NiMH batteries (1.2 vs 1.5 volts) the guide number is 80. 80 is a
full 2/3 stop less power than 104. So, assuming NiMH batteries at 10
feet, let's choose f/8 or maybe f/9 to be sure we don't blow the highlights.
The T-32 manual doesn't give guide numbers for other than ISO 100 but
you can easily compute them. Assume the real ISO 100 guide number is 80
and that yields f/8 at 10 feet. If you were using ISO 400 you know that
that is 2 stops more sensitive than ISO 100 so the exposure at 10 feet
would have to be f/16 instead of f/8. Run the numbers backwards and you
get a guide number of 16x10 = 160 at ISO 400. The same with choosing
ISO 50 (low ISO on the 5D) which we'll do for fill flash. The exposure
with ISO 50 would need f/5.6 instead of f/8 so the guide number for ISO
50 is 5.6x10 = 56.
With the 5D you have the option of going as high as 1/250 for flash sync
speed. We'll want to make use of that when we discuss fill flash but
for regular indoor flash you may want to make use of the ambient light
to help light the background and eliminate the tunnel look of
conventional flash. I sometimes use shutter speeds as slow as 1/4
second since the flash will pretty much freeze the main subject. I'd
suggest experimenting between 1/4 and 1/30 to see what you like and can
get away with.
Now to fill flash. The first thing you need to keep in mind for fill
flash is that now you're seriously combining ambient as the main light
with flash as the fill light. Ambient light exposure is affected by
aperture and shutter speed. Flash exposure (at a given power level) is
controlled by aperture and distance. Shutter speed doesn't enter into
the flash exposure except insofar as you're limited by sync speed.
What this means for fill flash is that you need to first set the ambient
exposure. If you're in fairly bright sun you will generally find it
advantageous to set the lowest ISO and highest sync speed on the
shutter. This will result in the largest aperture for the ambient
exposure which is one of the controlling elements for the flash
exposure. Let's assume a sunny 16 scenario at ISO 50. The base
exposure is 1/50 at f/16 which we can convert to 1/100 at f/11 or 1/200
at f/8 or 1/250 at f/7.1.
Given this light, ISO and max sync speed you are now locked into an
aperture of f/7.1 and this aperture must now be applied to the flash
calculation. Since we said the true guide number for a T-32 at ISO 50
is probably 56 we can determine a *main light* flash *exposure distance*
as 56/7.1 = 7.9 feet. Call it 8 feet, I can't estimate 7.9 feet :-)
But, we don't want a main light exposure, we want a fill flash exposure.
We want an exposure from the flash which is about one stop less bright
than the ambient light. The easiest way to calculate that is to leave
the camera at ISO 50 and do the flash calculation based on one stop
greater sensitivity or... back to ISO 100 for the flash. Now we're back
to a guide number of 80 instead of 56. The new distance calculation is
80/7.1 = 11.3 feet. Call it 12 since I can't estimate 11.3 and I'd
rather a little less fill flash than risking too much.
There you have it. Without being able to readily vary the flash power
you must accept that your distance is fixed once you've determined the
aperture. A zoom lens is to be greatly desired since you need to use
the zoom for framing if you can't zoom with your feet.
A flash such as the Sunpak 422D is much more valuable than a T-32 in
this situation since it has a 5 stop power range and it's manual flash
calculator panel is much more sophisticated than the T-32's. It allows
me to do everything I've done here using just the sliders on the panel
and for any power level. My Sunpak 422D's true guide number is even
less accurate than the T-32. Its true guide number is about 70 vs the
claimed 100... or a full stop less than claimed vs 2/3 stop less on the
T-32. But that can be corrected for by lying to the flash about the
selected ISO. I'd set the calculator panel at ISO 50, the same as the
camera, knowing that the flash is going to deliver one stop less light
than claimed or exactly the difference I'd like for fill flash.
One final point. If you are using the flash outdoors and the subjects
are in shade with full sun in the background this is not a fill flash
situation. You need to set the ambient exposure for the sunlit
background to avoid it being blown out [but still within the confines of
the sync speed]. Then the flash exposure is a main light exposure to
bring the subject brightness out of the shade and up to the level of the
background. I do that with a meter. I'll have to stop and think real
hard about how to do that without one.
Cheers,
Chuck
Phil wrote:
> Ali
>
> There are various ways you can use flash to aid you on a bright day and
> depends what equipment you use/have.
>
> Where possible I use my flash off camera manaul mode with radio slaves but I
> will presume these were not available
>
> In the shot below I used the sun as a hairlight and my SB80 as a fill, it
> was off Camera but could just as easily have been on Camera, you can in fact
> use the sun any way you wish depending on where you place your subject. I
> metered as per normal (manual) set flash to half power
> and did a few test shots and adjusted accordingly.
>
> The flash I always use in manual and I know roughly what settings to use
> following testing, by using manaul you get consistent exposures. The only
> limitations can be the Camera sync speed, the shot below was 1/160 at F4,
> ( I can creep above my sync speed to 1/250 with no adverse effects) I wanted
> to shoot as wide open as I could for the bokeh, I needed to drop the ISO
> down to 50 to get this reading. If the aperture was smaller you need to have
> the power in your flash to match.
>
> As for white balance, I shoot raw and tweak in ACR but if using flash
> normally set manually at around 6000K
>
> Dr Flash will explain all of this far better than I have :)
>
> http://i104.photobucket.com/albums/m187/deck-it-out/bun.jpg
>
>
> Phil
>
>
>
>
>> Not sure if this falls under a "Dr. Flash" request but
>> I had a question on using flash outdoors on a bright
>> day. I am a little confused about shooting w/ a flash
>> in sunlight to remove harsh shadows. I used flash
>> outdoors while shooting a model during a recent
>> outing. Some of my photos were overexposed. The skin
>> was sort of "washed out". My camera highest sync speed
>> is 1/200th.
>>
>> Does a diffuser do anything outdoors on a bright day?
>>
>> Should I mess with the white balance while shooting
>> outdoors?
>>
>> Should I even use a flash outdoors on a bright day?
>>
>> Thanks.
>
>
>
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