To get a black background on a photo is easy, set your camera to manual go to f22 with a shutter speed of around 200/ 250, then find a flower that's not got a lot of background something like a Tulip, and take your first shot, everything will be black, then set your flash to manual at full put it over the flower and take your next shot. If it's too bright drop the flash strength a bit, and if it's too dark lower the shutter speed.

Hi Graham,
Not quite getting this, the 2 photos have they got to be merged in Photoshop.
Many Thanks