D800 performance at ISO 50

<p>Does shooting at ISO 50 on a D800 provide any performance advantage over shooting at 100, such as expanded dynamic range, sharpness, reduced noise, other? I recently read one review which indicated that shooting at ISO 50 is basically akin to putting an ND filter on, thereby reducing shutter speeds, but that there are no other gains to be had compared to shooting at 100. Can anyone clarify?<br>

Thanks,<br>

Andrew</p>

<p>Most, if not all, the cameras that have a "lo" mode do NOT improve performance when you use it. In fact they almost always degrade it somewhat. It's an "emergency" mode for when you have too much light and you are better served by an ND filter.</p>

<p>I wish you could turn it off so you can't get to it on my cameras.</p>

<p>The base ISO for the D800 is ISO 100. If you go below that, i.e. Low 1, you may actually lose a bit of dynamic range, although the difference is small and therefore hard to notice.</p>

<p>Well, <a href="http://www.dxomark.com/Cameras/Nikon/D800---Measurements">DxO</a> show the same ISO for "50" vs 100. I've not checked on my D800, but I believe all that typically happens is that the camera takes an ISO 100 capture, deliberately overexposed by a stop, then there's a marker stored in a raw file that indicates the needed exposure shift. I believe it's just shorthand for "ISO 100, EC -1.0", except that the JPEG output and default raw converter behaviour will invert this exposure compensation. The overexposure means that you lose some highlight detail compared with a true ISO 50.<br />

<br />

Incidentally, DxO have <a href="http://www.dxomark.com/Reviews/Nikon-D810-sensor-review-New-DxOMark-leader/Nikon-D810-versus-Nikon-D800-versus-Nikon-D800E-Outstanding-performance">just published</a> a D810 sensor review. That really does have an ISO 50 (or 64, or whatever) and it seems to have a bit more dynamic range at that ISO than the D800 does at ISO100. Which was the point, obviously. (It actually seems to do very slightly worse from ISO200 to ISO1600, but only fractionally.</p>

<p>Most DSLRs, when shot in RAW mode at their base ISO, provide somewhere between 1.5 to 2 stops extra "headroom" over what would be rendered pure white in a JPEG capture. Setting a Lo ISO (in this case 50) simply uses up some of that headroom and transposes it downward for the JPEG. As far as I can see it does next to nothing with the RAW file, apart from alter the metadata attached to the file so that a 1 stop exposure compensation is applied by default.</p>

<p>The "Lo" and "Hi" settings on DSLRs aren't proper ISO settings, which is why they're not given numbers. ISO settings require the image quality to meet certain standards, albeit quite lax ones, set down by the International Standards Organisation. So if the camera maker doesn't give an ISO number to a sensitivity setting, you can be pretty sure that there's some loss of quality at that setting.</p>

<p>FWIW: The extra headroom in RAW is there, I believe, to prevent saturated colours from becoming posterised after the required colour space and logarithmic tone curve are applied to the linear sensor data. In most cases the spare dynamic range is fully useable with a RAW file when all three channels receive a similar exposure - white clouds for example. In extreme cases of colour saturation, or white balance, it can't be fully utilised without some colour distortion occurring.</p>

<p>"Does shooting at ISO 50 on a D800 provide any performance advantage over shooting at 100" - In short, no!</p>