Canon E-ttl System
Q. For those that use Canon systems, what’s your secret for using a
single speedlite either on-camera or on-a-bracket-on-the-camera, in a dark venue?
Evaluative or Average? FEL or no FEL? I try to consistently do the
same thing with each shot, dragging the shutter as much as is reasonable and
using FEL, but about 1/3 of my shots are either about 2 stops over or 4 stops
over. I’d like to achieve better consistency.
Is anyone able to get consistent results from the Canon Wireless Flash system?
If so, are there any special techniques that you’ve found to be especially helpful?
OK, the canon e-ttl system is extremely accurate, but often misunderstood and
misused. What I mean by that is the system itself actually takes a full
shot by flashing the speedlights in a preflash at 1/32 power and looks at the
actual result of the lights firing and determines the ideal settings for the
full power shot, which means its not guessing, it sees what the lights are doing
and than tells each light how much light to fire at the actual exposure while
the shutter is open.
WOW! That’s Great!
However, cameras do not know what you want the picture to look like and are
attempting to make the entire image average 12% gray in overall luminance, unless
you have dialed in a compensation factor at which it is attempting to make the
image 12% plus or minus the compensation factor. This changes with different
metering modes as a center weighted meter will tell the camera that the whole
image should be equal to x, but the middle is more important and that should
be given more priority so look at the whole frame and try to get as close as
possible to the correct exposure but give up or add more to ensure that the
center weighted area is in the right value. Same goes for spot only that
gives priority to a smaller point in the frame.
So what’s the problem?
Well the camera does not know what it is shooting, sadly while they can detect
faces, and look for smiles (well some of them) they are not yet able to
tell a bride from a polar bear or a groom from a penguin
Well it seems that many are shooting with these and not taking advantage of
a special feature called FEL or flash exposure lock, that can guarantee
a perfect exposure every time with flash because you can focus in close on skin
and fel which fires a preflash and meters and if you know you want skin say
2/3 over you can dial that in and that exposure will be held by the camera for
the next shot and can be held for several even if you recompose. And even
if it is totally wrong it will still give you the same amount of light as long
as you hold the FEL in the system. Why doesn’t everyone use that it sounds
great! Well it is great, but its not the most practical or even usable
at times when things happen fast and you need spontaneity.
Now what is the typical scenario? you shoot a bride in a white gown and
the face gets all dark and muddy, and the dress is dull and gray. or you
shoot a groom in his black tuxedo and the face is too bright and the tux is
a nice gray tone that seems to match the brides new dress. What went wrong?
Framing and a lack of the correct metering mode or not enough points to place
the spot meter on the face of the subject which is likely the more important
part of the shot and often very near to the 12-18% gray tonality that we all
seem to be looking for with out meters. What the camera did was it fired
a preflash and looked at a mainly white dress and determined that the image
was brighter than the standard 12% and darkened it with the exposure/flash settings
to make the image a happy mid gray in tonality, and for the groom in the black
tuxedo the camera looked and said its way to much black and it needed to brighten
the image through either exposure settings or flash power, and it again gave
you an image that is overall a nice mid gray in overall tonality.
How do you fix it? Well you can spot on the face and set metering to spot
metering, you can set manually but that kind of defeated the purpose of using
the e-ttl system, or you can use center weighted metering linked to focus point,
of course you can use FEL, and another option is to think ahead of what you
are shooting and adjust the flash compensation manually, if shooting predominantly
a frame fill with a white gown lower the flash exposure, or if its a dark
scene brighten the flash exposure to the desired level.
Newer e-ttl also include a good old distance reading in there. What that
does is say at x feet this much light hits the subject and once it knows how
many feet from the subject you are based on the focus distance supplied by the
lens (not all lenses and not all speedlights are compatible) it knows exactly
how much light to put out to get a specific exposure (it varies this based on
any compensation settings you may have adjusted) and that is always accurate
so long as there is nothing blocking the light from hitting the scene.
Flashes like the Vivitar 285hv use a different approach they have a sensor in
the flash itself that flashes until it gets enough light bounced back and shuts
off the flash, that amount is determined by the settings you place on it like
f5.6, f8, f11 at the given iso. This is accurate and works well
and does not take into account what the camera is seeing but rather how much
light is hitting the subject and returning to the flash. Main issue here
is that they were designed with a tolerance for negative film and allow a variance
of 1 stop over 1 stop under. Shooting slides or digital with the camera
set to the same as the strobe will likely show you a result that is approximately
1/3rd perfect exposure, 1/3rd under exposed up to a stop and 1/3rd over exposed
up to a stop. The latitude of film and raw can easily correct for this
but its not the ideal if you are shooting weddings or events and have hundreds
of images to proof. Wedding photographers have used this for years with
negative film and never knew of the issue and now see it while shooting digital,
why? because for most of them the lab processed and printed the film and
adjusted the exposures for the correct overall values. But this is getting
away from speed lights in general and off topic here.
To Learn more Check out some of my workshops here, or look into some of the great workshops that Canon puts on at http://www.learn.usa.canon.com/live_learning/workshop_main.shtml
©Stephen Eastwood 2008 www.StephenEastwood.com