So you're saying after Photoshop the highlights will be exactly the same from an overexposed shot at 200 (which meters at 100), as one shot at Lo 1?
I'm saying no matter what you do, it is always an ISO 200 sensor.
Higher ISO amplifies it digitally (multiplies data values), same as a boost in photoshop does. This amplifies the noise as well, either way. It is not more sensitive, it merely lies about the value it saw, and shifts it higher.
LO 1 just cuts the gain to be less than one, shifts it down lower (than the actual ISO 200 sensitivity). This reduces the dynamic range (Nikon calls it contrast, which it is), since technically there cannot be detail in the top half of the shifted histogram. Everything has been divided by two. That's the way it is always explained.
But if you intentionally overexpose a LO 1 picture, the picture looks awful, but the top half of the histogram is not blank (top half speaking linear... but we cannot see linear RAW). It does show data and spike in the top. So the histogram is not showing the data as shifted. Or rather, it is like the histogram scale is shifted along with the data, so it still looks like the unshifted values. Which seems useful, I'm sure this eliminates many customer complaints about an empty histogram. :smile: Just my notions, I don't know for sure.
I have not tested to carefully properly expose a picture at LO 1, and another carefully overexposed one stop at ISO 200 (same lighting setup), and then shifted the latter, and compared it to the former. I feel sure the histograms will appear different, but I have not looked at the image itself. I have just believed Nikon, but I should do that. The detail is not lost, just shifted down, but there is nothing left in the top half, so the dynamic range and contrast is less. Top half of a gamma encoded histogram is about 187 to 255. So hard to detect in the detail, but side by side, the contrast should appear to be lower, if it had full contrast in the first place.
What is clear, Nikon specifically does not call it ISO 100, and they do specifically recommend ISO 200 or higher, at risk of "contrast". Conceivably, a low contrast scene may not matter.