What do you considering the upper limit for ISO?

"RichA" wrote in message
...
Lets say you aren't pretending, like so many do that you can take
really good images at high ISO. Where do you draw the line? Canon
and Nikon are now boasting 100,000+ ISOs for their latest offerings,
the Canon isn't even FF! But lets say you shoot with a D700 and you
have the luxury of going with either 3200 or 6400 ISO. Can you
produce a shot worthy of keeping at 6400 ISO? Or are we just kidding
ourselves that the output at that ISO, or from any camera is
acceptable?
I shoot a D300. IMO, beyond 800 ISO I have trouble accepting the
images as really good. I'm talking about non-noise reduced raw
images. Sometimes, it's possible to use NR and not make the picture
look like crap, but the leeway is narrow.

As the sensor approaches perfection (i.e. all incoming photons caught) then
the issue will boil down to: -

1. Noise - how often with the sensor see photons that aren't there or
arrived by other means (e.g. cosmic rays). This problem affects computer
memories (the former the original Intel 1103 and the latter current large
memories with nanometre cells.

2. Quantisation - at very low levels the number of photons per colour, per
pixel is going to be small. This will lead to steps in level that will be
very noticeable in the image (as with DTT, but there it is low bits per
pixel).