I was pretty happy how slides were scanned with my BenQ ScanWit 2740S and Ed Hamrick's VueScan. Then I made pictures of the nightsky. I pointed my EOS-300 camera with 300 mm lens and opened the shutter manually for seconds. When I got the result home, it looked alright to the eye. Then I started scanning and encountered a problem: the black slides were completely gray. Time for a challenge...

Here we have one dark slide.

When scanned with VueScan on default settings (Color | Color balance = White Balance) , the result will be much like this: greyed out. Right you can see a detail of the scan. Notice how much details are blurred out.

Black point, white point
So let's go through some tips I got on comp.periphs.scanners. One tip that worked particulary well, was one of Gary Hundt, saying I should try to adjust the Color | Black Point % and White point %. I went to Color balance = Neutral and set Black point to 1 and White Point to 0, followed by a Brightness tuned down from 1 to 0,5 which resulted in the following image.

Increasing black point further
Does it help to increase black point even further? I tried black point 9. As you can see it appears to make dark parts darker, but light parts remain light.

Other techniques
How from here? Tom Harrison suggested to adjust the option Device | Lock exposure and possibly a Long exposure pass: