Just playing around a couple of days ago... The first picture is with the Sigma 120-400 at 400mm f/8. The roses are with the Nikon 18-300 at 230mm and 125mm respectively both at f/11. All pictures were handheld and all were light with natural sunlight. To get the black background for the roses I hung my old work jacket over the back of a kitchen chair and set the vase with rose on the seat of the chair.
For those of you who use Photoshop, (I use Photoshop CS4) I found an adjustment that helps get the background darkest black. It also helps set the brightest part of the picture properly.
In Photoshop from the pull down menu above the picture you are editing select Image then select Adjustments then select Levels. That should get you to the adjustments as shown above. See the little eyedroppers about midway down the right side? Click on the black eyedropper then go find the darkest part of your picture and click on it. Do the same with the white eyedropper and click on the lightest part of your picture. Suddenly the brightness and contrast are set just as they should be!