A while back, prompted by news of Nikon's new D4 that features the capability of shooting as low as ISO 50,[URL="http://dpnow.com/forum2//blog.php?b=291"] I reflected on the trend towards base-ISOs as high as 200 being the norm these days[/URL], but wondered if Nikon could be setting a trend that will see a return to much lower base ISOs.

So why would you want a low base ISO setting on your camera? My example in that blog post was the potential situation where, when using a fast lens in bright conditions - to minimise depth of field for creative purposes, perhaps - you could easily hit the limit of your camera's shutter speeds. But [URL="http://dpnow.com/forum2//blog.php?bt=829"]Louis Dobson responded just recently[/URL] to my post and, if rather dramatically, begged to suggest that I had missed the point.

And what point was that? Louis is very concerned that contemporary image sensor designs usually overlook performance parameters for low ISO sensitivity, probably because of pressures to deliver ever higher high-sensitivity performance at mind-boggling ISO settings. Forget about ISO 12,800, or 25,600, the new Canon EOS-1DX and Nikon D4 can be set to ISO 204,800, for example.

For a high resolution sensor to work well at very high ISOs it may have to compromise performance at low ISOs to avoid photosite saturation. Louis Dobson argues that this artificially limits the exposure flexibility you might expect from using low ISOs. Bright, contrasty, conditions can mean dark shadows where bright highlights have been preserved. The message I get from Louis is that too many cameras now limit the ability to recover shadows well even at low ISOs.

I think he has a point. I can't say it is an issue that perennially bugs me, but I think it's interesting enough to investigate. Have you encountered surprisinghly little flexibility in the ability to boost shadow levels without being punished by noise and plummeting contrast? Let us

know!