I am confused by this feature on the D300. I only shoot in RAW and 14 bits. If this feature really does increase the dynamic range, I should be using it on the highest setting all the time. However, I cannot imagine that it changes the sensor's response and any difference must be due to in-camera processing. If that is the case, can I forget all about it and rely on Camera Raw and Photoshop for processing? I can understand how j.peg or tiff files could be improved with this feature, but is there any advantage with RAW files that cannot be captured later?
The camera is young enough that not much is really known about how it really works yet.
You can gather clues, though. Try shooting something half black, and half white, with the camera set to Av-pri and Active D-Lighting. Take a shot where the frame is 20% white on one side, 40%, 60%, and 80%. Did the camera use the same shutter speed for all 4 images? If it did (and the same ISO, of course), then it is actively sensing the highlight brightness and is keeping it at a certain relative distance from the whitepoint.
Another clue; is it available at all ISOs? That might help figure it out.
RAWs can be helpful, but before you go posting a lot of big RAWs, we need to think of how to shoot the test, so you don't waste your time uploading big RAWs that don't help, somewhere. What I am trying to say is that if this feature *truly* is active, we may have to make sure you trigger it. It might do nothing, for instance, in a low-contrast scene, but do something in a high-contrast scene.