If you have a bendable-kneck desk lamp, point it at the subject, but make sure it is close to it. The farther away it is, the more light will come out of the lamp. Here's an example:
Notice that you cannot see the edge of the baseplate:
Infinite Darkness by rioforce, on Flickr
Here's how I did it:
Infinite Darkness Setup by rioforce, on Flickr
I tilted the lamp towards the camera so what's hitting the minifigure is actually so indirect light, not the direct light on the light bulb. That way, the light will fade out right before it hits the edge of the baseplate. Notice the shadow on the baseplate. That's where the light fades out.
Here's my camera settings:
Aperture: ƒ/5.6
Shutter Speed: 1/20
You probably already knew this too, because your pictures seem to show it, but make your your ISO is set to 100 and Active-D lighting is off (That lights up the background and ruins the infinity darkness look)
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