Wow, learned a valuable lesson on this. Was just playing around with Non-TTL auto mode* with an old SB-26 on a digital camera - it was a "what am I going to do if the SB-800 doesn't work and I still need on-camera flash?" kind of experiment. When I used this combo, I was getting shots that were about two stops overexposed, and I was a baffled as to why.
That was until I looked at the front of the flash, and noticed that the Non-TTL Auto sensor looked "fuzzy." There was a layer of dust on the sensor that was blocking about two stops of light the flash subsequently left the flash tube on longer to compensate. I cleaned the sensor with a Q-TIP and it works perfectly now.
*For those of you not familiar, the SB-26 is a 1990-vintage flash that doesn't have the TTL modes that work on a digital camera. It does TTL on film bodies, but not on digital. On a pro camera like the D1 - D5 (I think this feature is still on the D5), the camera will pick up that there's a flash attached and set the shutter to 1/60th (depending on you settings) and it will transmit the ISO to these old flashes, but you need to set the aperture manually on the flash. Therefore the best way to do this is with either aperture priority mode or manual mode. On the hobbyist and semi pro cameras, the camera does not set the shutter to 1/60th and it doesn't transmit the ISO to the flash, so you need to set both the aperture and the ISO on the flash and use manual mode on the camera. This also holds true for most of the other flashes made for film bodies.