James , Why don't you post this on the D80-D40 Forum?http://forums.dpreview.com/forums/forum.asp?forum=1034.
Put an example picture up and I am sure you will get an answer there. JerryNikon D60 18-55vr & 55-200vrSB400Casio Z750..
Here's a guess. In Tv mode you set the shutter speed to 1/20, fine. Suppose the correct aperture was f/4 (did you check?). If you have an f/5.6 kit lens the picture will be underexposed as the lens will not open to f/4. if you set Ev compensation to (say) an additional +2 stops to compensate, you are telling the camera to use an aperture of f/2. But...
You can dial in as much +ve exposure compensation as you like but the lens can't open any wider. Of course the camera could length the shutter speed, but in Tv mode you choose the shutter speed and the camera leaves it alone..
Try taking a meter reading and setting the correct exposure manually..
We need a lot more information in order to understand what was going on. We need to know the ISO, aperture, and Exposure Compensation value used on the G6. Only then can we have an idea of the actual exposure level..
That said, I really doubt that the G6 used a shutter speed of 1/400 at night. Even with the G6s fast lens, you still need a light level approaching shaded daylight to get a shutter speed of 1/400 sec..
If youre in shutter priority while adjusting EV and the scene isnt getting any brighter, that means that your aperture cant open anymore. What lens were you using? What was the aperture setting that the camera settled on?.
Without this info we just have no idea what was going on...
I am a bit confused by your question. How could you get 1/400sec at night?Even if using ISO800 it's too fast.What people?.
Anyway, I was there and took many night shots when the lights were shining on the falls. I used a tripod, and 1/10 ISO100.came out real nice.http://www.flickr.com/photos/rglukhoy/..
I hope that this will help you with your night shots.I took images there twice in the past month and got some great shots of thecoloured lights at night.For night shoots you need to shoot in AV or manual ... not TV.If you want to use Av ( it is the easiest for starting out) set the following:ISO = 100Aperature F/8.
Using the centre focus point, place it in the brightesss area of the falls to ensure that your auto focus will work and give you a sharp image or you could use manual focus..
After taking the first shot, look at your histogram and then change your exposure compensation to increase/decrease the shutter speed for your next shot....
This will get you into the general exposure area ... and then you can fine tune your exposure by examining the image in the LCD and the histogram while changing the exposure compensation...
I think Mike 703 is correct. If you are trying to expose at night or in very low light, shutter priority is the wrong mode to use. Aperture priority is the best way to go because you set the ISO and aperture (even low ISO and a smallish aperture) and the camera will choose a (lengthy) shutter speed. A tripod will be necessary and you should try a number of different levels of exposure compensation to improve your chances of getting the right effect..
If you set the shutter speed and ISO, the camera can only set the aperture to the maximum the lens will allow. If you are near or at that aperture with your choice of settings, increasing the exposure compensation will not change the exposure itself...