I just attempted to shoot my daughter juggling a soccer ball iin our garage and was using OCF. I wanted to black out the background and set the camera in full Manual mode with auto-flash. I made sure that I was about 4+ stops under Ambient without the flash and got nearly black bacground. But, with the flash, I could still see a bunch of the background (about 10 feet behind my daughter). Is there a better way to accomplish this? Why on some point and shoots is the background completely black when doing a 4-5 foot snapshot, but I couldn't achieve this here. I was not in HSS.
Move your flash in as close to the subject as possible. The closer the flash gets to the subject, the faster the falloff (it's the inverse square law at work).
The flash should auto-compensate as needed as you get closer. ETTL on Canon flashes can be a little finicky though so if it starts to under- or over-expose, just apply a little positive or negative Flash Exposure Compensation (FEC).
Since you're using off-camera flash, you can also try moving that light high (maybe 45-60 degrees to the camera-to-subject line, aim down, and add your own home-made snoot/gobo/flag to block the light as much as possible from the garage wall.
The flag/snoot can be out of black construction paper or something similar. Google "black foamie thing" and you will get the idea. A gridded soft-box would probably be ideal for this scenario; I am not suggesting you go out and buy one - just that the combination of large, diffuse but directed/controlled light would be a good way to think about this.
Basically what you have to do is not light the background. Any color will go black if there is no light on it. You get to this by moving the light either far away from the background or shoot at a low enough power so that the light doesnt reach the background. Like Steve said, its the inverse square law.
The way that I would go about doing this would have the subject as far from the background as you can get them, and then get your light source as close to the subject as you can. That way when you meter it, you can shoot at a lower power vs having the light source farther away and needing to shoot at a higher power.
Thanks. I just tried again. I put the speedlight about 3 feet from them at chest height a few inches back on flat surfact. I then shot down on them and got the desired effect. I think if I were in the gym, i would put the light down on the floor on upward aim and then shoot the player horizontally to make sure the background then was "under" the beam of the light.
Yikes... shooting up at someone with a speedlight on the floor is a guarantee for what we call "horror light". It will light the underside of the chin and nostrils, cast the eyes in deep shadow, and will not be at all natural-looking. If you're shooting in a gym, just get as far away from the wall as you need to kill any spill from your flash. Keep the flash up high and close, and use a shoot-through umbrella or a diffusion panel to soften and spread the light, and you should have a better exposure.
In a gym it should be really easy with a speedlight because you can get really far away from the background, and the speedlight wont have enough power to get to the background even if you wanted it to.
Use a fast enough shutter speed that no ambient light is seen by the camera then placing you main, fill, and separation lights so none of their light hits the background. You can use a plain white background and by removing all the ambient light by use of a fast shutter speed the bg will be pitch black, remove sovereign of the light you make it grey light with enough light and it is white , if you want a color bg ad gels to you bg lights or filters to your camera and correct the color for the subject. One way is referred to the additive Meath the other is call subtractive.
There used to be a link floating around hear where a famous British photog walks you throug lighting the bg at some type of photo users meeting. It is really good if you do not understand the theory
Something to be aware of when shooting in a small space is the "Spill Fill" variable. Where are the footprints of your lights hitting and reflecting off besides the intended subject? Is the footprint overlapping the floor and ceiling? Is your key light bouncing off the opposite wall? If so you will get spill fill.
If shooting on most backgrounds spill fill bouncing around the room isn't necessarily a bad thing because it helps create the same "wrap around" fill effect seen in indirect skylight outdoors. But if going for a totally black background the spill fill may be enough to turn it gray despite all the other suggestions above.
The solution? A larger studio space or black draping. My basement studio space is a finished room with shell white walls and a big mirror on one installed by the previous owner. When shooting on dark backgrounds and wanting to eliminate the spill fill variable I hang black fabic (flat king sheets from Walmart on the walls to kill it. I remove the drapes when shooting on white and desire lower overall contrast to get the wrap fill effect.
All the posts are great so far, and I agree with everything suggested.
I will throw out another idea however. You can try to limit the spill light that is not landing on the subject, but instead is lighting the background. Grids, snoots, and flags can all do this.
It seems like simply having a black background and enough distance for the light falloff. If the flash is a 3' and the background at 12' the falloff should leave 1/40th of the exposure on the background.
With enough distance or with good control of all the light, the background color does not matter much as mentioned above. But it can help a lot to have a plain black background cloth rather than a wall with complex stuff showing. The idea of a king sized black bed sheet from Walmart is a good one. The last time I bought them there, you could buy just the top sheet, and did not need to buy a set. The one edge has a wide hem that can be opened up at each end, and you can then put a support tube or even a rope through there. For not too much money, you can have an improvised cloth background, and a black and fairly flat one is easier to keep black than a lighter colored complex one.
A gridded soft-box would probably be ideal for this scenario; I am not suggesting you go out and buy one - just that the combination of large, diffuse but directed/controlled light would be a good way to think about this.