This may seem like a dumb question, but could someone explain why you would use speedlights in "groups?" Of course I understand the need and usefulness of several speedlights, but if they're all firing at the same time, then what's the need for groups?
#1. "RE: Why Groups?" | In response to Reply # 0
Covey22 Charter MemberThu 20-Mar-08 04:37 PM | edited Thu 20-Mar-08 04:38 PM by Covey22
You can specify the Groups to fire at different exposure values or power-levels. For example, a traditional two light setup flanking a posing subject would have the flash on the photographer's right fire at TTL levels as determined by the camera. The flash on the left would fire at half the power of the right side, because it's "filling" the shadows created by the main flash. So the right hand flash would be in Group A and the left-hand flash would be in Group B.
Here's a portrait example from Nikon showing such a setup. And here's another page explaining how the wireless flash system works. (Macromedia Flash Player required for both pages)
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#2. "RE: Why Groups?" | In response to Reply # 0
Wayne Registered since 05th Nov 2005Thu 20-Mar-08 04:50 PM | edited Thu 20-Mar-08 05:35 PM by Wayne
Groups are the units that are adjusted individually, that is the groups get unique command signals. Groups could have multiple lights in it, which then all get the same command signal (in the one group).
Try this to understand. Set up some simple table top scene, maybe your coffee cup, anything capable of casting a shadow on the table. Place one speedlight in Remote mode Group A at three feet from the subject, on one side of subject. Place another speedlight on the other side of the subject, but in Group B at nine feet from the subject. Measure this. This is 3x distance.
Now we know if the flash distance is 3x greater, and if the lights are equal power level, then the far light will contribute 9x less intensity, so that its exposure contribution will be over 3 stops down.. that is, the light at 3x distance will hardly contribute to this picture. This is simply the nature of flash, inverse square law, etc.
But in Remote mode, the CLS commander meters both groups (individually), and so sees and realizes that the far light must fire with much more power to equalize it, so that is what happens. The groups are equalized to give the same exposure at the subject. The final flash is fired together, but the preflash and metering are done individually (too quickly to see it). That is what groups are.
We can easily see this result happen if we simply look at a simple test like this. May take five minutes. You will never forget it.
Perhaps you dont want the two groups to be equal.. perhaps you want the main light light to be one stop stronger than the fill light... so set the group with the fill light to be -1 EV compensation, and it will be. Metered to be the same, then less one stop. We can see this result too.
Then also try to both lights in the same one group (assign both to group A and repeat - press shutter), and then the groups lights will get the same signals, and then the distant light will fail to contribute much - at least it will be in insignificant degree (in this 3x distance case). The strong shadow then will clearly show which light contributes and which does not. That is expected of course, but the point is to show the difference that happens when in different groups.
#3. "RE: Why Groups?" | In response to Reply # 0
fatmav Registered since 02nd Jan 2006Thu 20-Mar-08 09:01 PM
>This may seem like a dumb question, but could someone explain
>why you would use speedlights in "groups?" Of course
If you mean why put multiple speedlights in the same group, then the answers are usually shorter recycle time and also equipment preservation. The former is because less power is discharged from each speedlight and the latter is because we don't want to melt our speedlights...
A more exotic use would be to create a somewhat unique "catch" (the reflection of the light source in the subject's eyes). It can be quite interesting. Flickr has some photos demonstrating how the catch looks like when you use eight SB-R200 in a portrait.
#4. "RE: Why Groups?" | In response to Reply # 0
TObject Registered since 12th Nov 2004Fri 21-Mar-08 05:38 AM
Also in the M mode you can take advantage of the fact that all speedlights in a group would receive command to fire at the same power level. Thus, you can use that to fire say multiple SB-800s at the same power level even when the speedlights are far apart and light the subject differently.
As such, if you are using three groups, you can have much more then three speedlights creating very complex lighting setups. You would still be limited as to which of the three power levels to choose for each speedlight; but three levels is enough. Between that, and varying distance and modifiers, you should be able to do virtually anything, picture lighting wise.
#5. "RE: Why Groups?" | In response to Reply # 0
HBB Charter MemberFri 21-Mar-08 11:04 PM | edited Fri 21-Mar-08 11:12 PM by HBB
I'm the speedlight rancher with the herd of twelve SB800s that I use photographing law enforcement officers at night in various tactical situations.
I frequently use all three remote groups (A, B and C), plus the on-camera SB800 or SU800 and would love to have two or three more distinct groups (D, E and F).
With multiple groups, I can place supplemental illumination (speedlights) exactly where I want it and at the exact power level needed for the shot. Speedlight to subject and subject to camera distances vary all over the map. Some times one remote group will be in TTL mode and the other two in manual mode. With moving vehicles, long shutter times (six to thirteen seconds for example) and rear curtain sync, all speedlights will be in manual mode.
Night shots involving officers in very dark blue or black uniforms against very reflective white patrol cars present very interesting lighting challenges. I usually use one group to light up the dark uniforms, a second group to illuminate the patrol car and the third group for spot fill on the backs of heads or to illuminate a background object. I never know what will be needed until I set up the shot.
Hope this helps a bit.
HBB in Phoenix, Arizona
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