Why not slower ISOs?

wrote in message
...
Kibo informs me that "David J Taylor"
stated
that:
SNIP
Fuji have their dual-site CCD sensor, with the smaller
photodetector being
less sensitive....

Betcha they implement it by including the moral equivalent of an ND
filter over the extra photodetector. (Well, that's how I'd implement
such a system.)

Wouldn't bet on that. The smaller sensor(aperture) has a smaller
chance of being hit by photons during the same exposure time. If the
underlying potential well depth is large enough, it requires much more
energy to saturate. The difference is in the aperture size, which is
much easier to implement than unstable filters.

Bart

wrote in message
...
Kibo informs me that "David J Taylor"
stated
that:
SNIP
Fuji have their dual-site CCD sensor, with the smaller
photodetector being
less sensitive....

Betcha they implement it by including the moral equivalent of an ND
filter over the extra photodetector. (Well, that's how I'd implement
such a system.)

Wouldn't bet on that. The smaller sensor(aperture) has a smaller
chance of being hit by photons during the same exposure time. If the
underlying potential well depth is large enough, it requires much more
energy to saturate. The difference is in the aperture size, which is
much easier to implement than unstable filters.

Bart

Roland Karlsson wrote:
Ian Stirling wrote in news:414e2ff1$0$69721
:


http://www.fillfactory.com/ do some.
The sensor is linear up to a certain limit, then non-linear up to a much
higher one.
This of course trades a bit of tonal resolution for a much, much higher
range of intensities.

Thx. According to their site, they have stopped
supporting non linear sensors.

There was one range that was specifically advertised as high
dynamic range.
However, look on the other datasheets for "dual-slope dynamic range
expansion", which is the same thing.

Roland Karlsson wrote:
Ian Stirling wrote in news:414e2ff1$0$69721
:


http://www.fillfactory.com/ do some.
The sensor is linear up to a certain limit, then non-linear up to a much
higher one.
This of course trades a bit of tonal resolution for a much, much higher
range of intensities.

Thx. According to their site, they have stopped
supporting non linear sensors.

There was one range that was specifically advertised as high
dynamic range.
However, look on the other datasheets for "dual-slope dynamic range
expansion", which is the same thing.

I own an Olympus C765 which has ISO settings from 64 - 400 so some
manufacturers are attempting to address this problem

Nancarrow

jpc wrote in message ...
On 18 Sep 2004 17:24:38 -0700, (Bob
Alexander) wrote:

A short time ago, I was photographing a waterfall, fiddling with
neutral density filters (screw them on, screw them off, be careful not
to drop them, make sure they're clean, etc.) and I thought that life
would be a lot easier if a digital camera had arbitrarily low ISO
equivalent settings, e.g. ISO 50, 25, 12.5, 6.25, etc. We would all
save the expense and trouble of buying and using ND filters.

I know that high ISO equivalents introduce problems with noise, but is
there any technological reason digital cameras don't have low ISO
settings, or is it just that no one has thought of it yet?


Digital sensors have a "single' as in 'one and only one' ISO rating.
It's determined by the number of quanta that fill a sensor well to
saturation. Everything else is only gain settings like in "turn up the
boom box, man," gain settings.

Since the true and only ISO setting is fixed by the physics and
engineering of the sensor, the simplest way to get the equivalant of a
lesser ISO is to toss a ND filter in front of the lens.

jpc

"nancarrow" wrote in
news:1095794247.CGeRS83kOcLcJCSbcTTqOg@teranews:

I own an Olympus C765 which has ISO settings from 64 - 400 so some
manufacturers are attempting to address this problem

ISO 64 is not unusual for compact digicams, my G2 has ISO 50.

The poster wondered why not arbitrarily lower, e.g. ISO 12 or 6 or ...

The answer is that a (normal) sensor has a natural ISO, which is the
lowest possible without using optical filters. Your camera seems
to have an ISO 64 sensor.

The higher ISOS you get by increasing the gain before doing
A/D-conversion. That is possible - but it introduces more noise.


/Roland

"nancarrow" wrote in
news:1095794247.CGeRS83kOcLcJCSbcTTqOg@teranews:

I own an Olympus C765 which has ISO settings from 64 - 400 so some
manufacturers are attempting to address this problem

ISO 64 is not unusual for compact digicams, my G2 has ISO 50.

The poster wondered why not arbitrarily lower, e.g. ISO 12 or 6 or ...

The answer is that a (normal) sensor has a natural ISO, which is the
lowest possible without using optical filters. Your camera seems
to have an ISO 64 sensor.

The higher ISOS you get by increasing the gain before doing
A/D-conversion. That is possible - but it introduces more noise.


/Roland

"nancarrow" wrote in
news:1095794247.CGeRS83kOcLcJCSbcTTqOg@teranews:

I own an Olympus C765 which has ISO settings from 64 - 400 so some
manufacturers are attempting to address this problem

ISO 64 is not unusual for compact digicams, my G2 has ISO 50.

The poster wondered why not arbitrarily lower, e.g. ISO 12 or 6 or ...

The answer is that a (normal) sensor has a natural ISO, which is the
lowest possible without using optical filters. Your camera seems
to have an ISO 64 sensor.

The higher ISOS you get by increasing the gain before doing
A/D-conversion. That is possible - but it introduces more noise.


/Roland

jpc wrote:
On 18 Sep 2004 17:24:38 -0700, (Bob
Alexander) wrote:


A short time ago, I was photographing a waterfall, fiddling with
neutral density filters (screw them on, screw them off, be careful not
to drop them, make sure they're clean, etc.) and I thought that life
would be a lot easier if a digital camera had arbitrarily low ISO
equivalent settings, e.g. ISO 50, 25, 12.5, 6.25, etc. We would all
save the expense and trouble of buying and using ND filters.

I know that high ISO equivalents introduce problems with noise, but is
there any technological reason digital cameras don't have low ISO
settings, or is it just that no one has thought of it yet?


Digital sensors have a "single' as in 'one and only one' ISO rating.
It's determined by the number of quanta that fill a sensor well to
saturation. Everything else is only gain settings like in "turn up the
boom box, man," gain settings.

Since the true and only ISO setting is fixed by the physics and
engineering of the sensor, the simplest way to get the equivalant of a
lesser ISO is to toss a ND filter in front of the lens.

jpc