Sun 29-Jul-12 04:46 AM | edited Sun 29-Jul-12 04:48 AM by gpoole
I don't have a D700, but I believe my D300 should behave similarly. Also my D800 is at Nikon for repair, so I have no way to make a comparison.
I just verified the behavior of my D300 in Manual and Auto ISO. I just pointed the camera a lamp in my family room and started turning the dials.
If I decrease exposure, the ISO increases until it hits the limit. If I continue to decrease exposure the meter indicates under exposure. It doesn't matter whether I change the exposure with the aperture or shutter speed.
If I increase exposure the ISO decreases until it reaches the base ISO. The ISO will go below the ISO I have set, but Auto ISO will not select a Lo ISO setting. It doesn't matter whether I change the exposure with the aperture or shutter speed. If I use a small aperture I can set the shutter speed to times longer the the minimum Auto ISO setting and still see the ISO change as expected. I believe the minimum speed only applies to A and P modes.
This is how I remember it working in real shooting situations.
In Thom Hogan's D800 eBook, he says in A or P mode the camera will go below the minimum shutter speed when in hits the max ISO. In the same section he says previous cameras would just underexpose instead. He doesn't say that the manual auto ISO behavior of the D800 is different from the previous models.
If your camera exposes properly in other situations, I can't believe you have a camera problem. The operation of Auto ISO is in the firmware and uses the same sensor and camera switch settings as the non Auto ISO modes. If you have a problem only with Auto ISO in Manual mode, then I think it must somehow be a problem with your settings or a fallacy in your experiment.
I don't know the history of D700 firmware updates, but I'd strongly recommend updating to the latest version if you aren't already there. Possibly Nikon had a firmware bug that could cause improper auto ISO operation. As a retired computer programmer I cannot believe that you can have a firmware error that would only effect Auto ISO. If your firmware somehow became corrupted, then you would have a whole slew of problems.
Gary in SE Michigan, USA. Nikonians membership - My most important photographic investment, after the camera. D4, D810, D300 (720nm IR conversion), D90, F6, FM3a (black), FM2n (chrome) YashicaMat 124, Graflex Speed Graphic 4x5 My Nikonians Gallery & Our Chapter Gallery