Is 50 ISO even real?

Or is it just "cut the voltage" in order to allow slower shutter
speeds, wider lens openings,
etc? Most cameras show no improvement going from 100 to 50 and a
couple I've read about
actually produce worse output at 50 than 100. So is 50 ISO simply an
electronic "neutral
density filter" in most cases??
-Rich

It was on my Olympus C8080 as well, but Nikon DSLRs started at 200 and
some cameras
now don't go below 100 so I assumed that was the "base" sensitivity of
those sensors
and that 50 ISO was merely a reduction in signal of some kind and not
a true sense "floor."

Rich wrote:
Or is it just "cut the voltage" in order to allow slower shutter
speeds, wider lens openings,
etc? Most cameras show no improvement going from 100 to 50 and a
couple I've read about
actually produce worse output at 50 than 100. So is 50 ISO simply an
electronic "neutral
density filter" in most cases??

Way too complex a question to be asked seriously by a chap who posts
only to create threads.

If you really want to know, "Rich", you could Google this very
newsgroup. It was covered ad nauseum within the last few months.

--
John McWilliams

All sensitivities work like that.

Rich wrote:
Or is it just "cut the voltage" in order to allow slower shutter
speeds, wider lens openings,
etc? Most cameras show no improvement going from 100 to 50 and a
couple I've read about
actually produce worse output at 50 than 100. So is 50 ISO simply an
electronic "neutral
density filter" in most cases??
-Rich

It is real on the 1D Mark II, although not quite.
At ISO 100 the sensor max is 53,300 electrons.
So at ISO 50, one would expect 106,000 electrons, but
the sensor saturates at 79,900 electrons. So really the
lowest ISO is 67 (100 * 53300/80000).
http://www.clarkvision.com/imagedetail/evaluation-1d2

On smaller pixel cameras, which collect fewer photons, ISOs
below 100 are reasonable. It all depends on the % active area,
full well and quantum efficiency. The Nikon DSLRs with a CCD
sensor appear to have a slightly higher quantum efficiency,
thus the higher minimum ISO. I'm analyzing a D50
now and will have results soon.

Roger

Isn't hindsight wonderful? Makes you feel really....superior.

"Rich" wrote in message
oups.com...
Isn't hindsight wonderful? Makes you feel really....superior.


Not difficult with you buster.