By playing with the exposure settings, the background can be darken to the point where your subject seems to be in complete darkness. Why? Because the subject is the most highly lighted by the narrow light beam of the halogen lamp and all other things around it are faintly lighted by the available light. By setting the parameters on your camera to have your subject perfectly exposed, the environment will then seem underexposed for your camera sensor.

To modify the settings, you have to put your camera on manual mode (‘M’). You can change the aperture size (f+number) and/or the exposure time according to these simple facts:
-Aperture: lower value -> more light is entering your camera
-Exposure time: lower value -> less light is entering your camera.
For this example, I have only modified the aperture size (from f2.8 on picture#3 to f7.1 on picture#7).

As you can see on pictures 3 to 7, by decreasing the exposure (amount of light captured by the camera’s sensor), the subject is going slowly from the overexposed state to the underexposed and the background goes darker and darker.

If you don’t want to sacrifice your narrow depth of field by decreasing the aperture (higher f number), then you may want to decrease the exposure time.

When your subject reflects a lot of light, you should not target it directly with the light beam. Instead, put the center of the beam a few inches from your subject.

You may also want to move the telescopic lamp to produce shadows.

For a black background, the picture should be taken in a room with no window, or at night with the same technique as the one described above.

Notes:
-The aperture size has also effect on the depth of field. The lower the value and the narrow depth of field you will obtain.
-The pictures below are numbered in the order you should look at them.