Remember that negatives (B&W or colour) will, by definition, have a very low density range; you actually want a compressed histogram, which you then use curves to expand out into a range of intensities. A negative is not simply an inverted positive; you have to map the proper contrast yourself.
As for the light source, I use a Artograph Lightpad, and it gives very even illumination.
IMAGE LINK: https://flic.kr/p/q2KGSi eastside by vracing, on Flickr
Before, the shape of the historgram is like a skinny, inverted V shape. Well, I think this is it. I think I nailed it. The final puzzle is that I still need to use Vuescan to invert my DSLR scan negatives. With CS5, certain scene is easier to invert. Others, I had troubles with last night because of some stupid color casts. With Vuescan, I just load the DSLR scan copy and to scan. Vuescan would automatically invert it and to save it. Then, I would just edit the shot normally in CS5, which is a lot better and faster than tweaking the black and white points and trying to color balance the shot.... Of course, my goal here is to do these DSLR scans without using another reference shot to match it. And to get the tone curves and the tonality right as well.
Here is another example. No HDR here just single exposure with 2 shots stitched. This is from the DSLR scan. The highlight here is very intense enough coming off the water treatment plant. The original shat has that glow and some flares too. Yes, at 100 crop, you can see the individual metal railing by the ladders on those chimneys.
Original shot scanned with the Canon 9000f.
IMAGE LINK: https://flic.kr/p/pAqMK8 pipes by vracing, on Flickr