need hellp with lighting backgrownd

[Cherepashka]

can anyone explane how can i, and or can i at all underexpose backgrowng in light room? here is one picture, now how should i take this shhot to get backrown dark (even almost black) but person, as it is? thank you a lot!!!

[iLuveKetchup]

What's your setup? The quick answer is to stop down your aperture.

[Cherepashka]

oh,set ups... i am so new in lighting... have two elinchrome strobes and just playing arownd with them, but never get right (with underexposing backgrownd) !

[Franko515]

I believe if you put more distance between the subject and background then move the light closer to the subject the background will go dark or black if you like.

http://photography-on-the.net/forum/showthread.php?t=273380

[MrScott]

Well in that 2nd pick you outed the sun in the window behind the subject. Turn the lights down or look into some other light modifiers that control and direct the light rather than spreading all over the room.

Alternate reading...
http://www.flickr.com/groups/strobist/discuss/72157600474102331/

[Cherepashka]

thank you, guys, a lot!!!

[FlashZebra]

Radically increase the distance from your subject to your background, while maintaining the subject to camera distance.

At the same time, decrease the distance from the flash to the subject.

Both of these adjustment will really decease the amount of light falling on the background, relative to the the amount of light falling on the subject.

Enjoy! Lon

[Wilt]

The flash to background distance is key, as others have stated. However, key information has been omitted:

On your camera, there is no way to control the relative brightness of subject vs. background in a meaningful manner...you MUST have your light off the camera! Then you can control the relative distance of light--to-subject vs. light-to-background. Let's illustrate...

Imagine your camera-to-subject is 8' (so field of view with 30mm on your APS-C camera is about 5.5' wide, like your example); also let us assume your camera-to-background is 11'. The first principle to remember is that you can treat distances as surrogates for f/stops...so light from on-camera flash is 1EV brighter at 8' than it is at 11' ...f/8 vss. f/11.

If you move closer (subject is 4', background is still 3' farther at 7') it is still 2EV different in brightness.'''...f/2.8 vs. f5.6... But that also changed the framing of your shot and the perpective to objects surrounding and in the background, which might not be acceptable to you! Now, instead, imagine your camera-to-subject is 8' (so field of view with 30mm on your APS-C camera is about 5.5' wide, like your example); also let us assume your camera-to-background is 11'. You leave your camera there, and separately put a light 3' from the subject (and 6' from the background). Now the light is about 2EV different in brightness (subject vs. background)... f/2.8 vs f/5.6...and your camera is still in the proper location for the shot you want to take!

Better yet, move the subject, relative to the background. If you keep the camera-to-subject constant at 8', but have moved the subject farther from the wall in the background, that alters the relative brightness even more...if the subject moved forward 4', she is now 7' from the background. So if light-to-subject stays 3', light-to-background is now 6', and the relative brigtness of the two is 3.5EV or near black!

[TMR Design]

The suggestions offered are all good ones but for the particular shot you've posted it appears to be in a home and there is furniture that I imagine you're not going to be moving around for the shoot. In that case you really don't have the option of moving the subject further from the background and you're most likely going to have to move your lights closer to the subject and positioning them so you have as little spill in to your background area as possible. This will create greater separation between subject and background and will allow for proper exposure of the subject while causing the background to go darker.

[Cherepashka]

thank you, guys, a lot!