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Re: Why no ISO <100 ??

 
 
ransley
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      07-03-2008
On Jul 3, 2:23*pm, "simon steel" <(E-Mail Removed)> wrote:
> Ok...
> Higher ISO means more noise - we all know that...
>
> But why don't cameras come with an ISO lower than 100?
> Is there some trade off in image quality below the benchmark ISO100 figure?
>
> not all of us want higher shutter speeds... some of us would like to slow
> down the the shutter speeds..
>
> SS


I will guess its just a benchmark of what is easily usable handheld, I
used to shoot 25 asa- iso Kodachrome and very often a tripod was
needed with a slower lens, Kodachrome was once 15 asa - iso so it was
even more demanding, they could rate-make the sensor slower but I will
guess they make the sensor optimal at 100 for ease of use.
 
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David J Taylor
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      07-04-2008
simon steel wrote:
>>> My guess it the OP wants to trade of ISO "speed" for less noise. >>

>
> I actually would like to shoot slower speeds without need for
> filters... Had not realised that noise would also be an issue with
> sub-100 ISO setting.
> Was really just curious as to why the min speeds in my DSLRs are 100
> and 200 [Pentax K10D and istDL]
>
> ss


Simon,

It's as Doug said - the sensor will saturate when fed too much light, so
get use lower speeds you need an ND filter. You /could/ make a less
sensitive sensor, with ISO 25 as its lowest speed, but then its highest
usable ISO would be proportionately reduced, and the camera would be less
attractive to many....

David


 
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David J Taylor
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      07-04-2008
Alfred Molon wrote:
> In article <H8jbk.20475$(E-Mail Removed)> , David J
> Taylor says...
>
>> It's as Doug said - the sensor will saturate when fed too much
>> light, so get use lower speeds you need an ND filter. You /could/
>> make a less sensitive sensor, with ISO 25 as its lowest speed, but
>> then its highest usable ISO would be proportionately reduced, and
>> the camera would be less attractive to many....

>
> They could make a multiple exposure sensor, i.e. a sensor exposing
> four times the image and averaging the images. Would give lower noise
> and an ISO equivalent to 25 (4 x the exposure time).


We had a discussion about this possibility recently - in connection with
capturing specular highlight details.

Cheers,
David


 
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John Sheehy
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      07-04-2008
"dwight" <(E-Mail Removed)> wrote in
news(E-Mail Removed):

> My Canon S3IS also has an 80 ISO, but I rarely use it other than a
> bright sunny day. And I don't care for the results at either ISO400 or
> 800, so I'm pretty much stuck at 100 or 200.


> Good thing it has the IS...


.... and it makes the IS' job much simpler when some big, heavy mirror isn't
slapping around. Even without IS, I get sharper images at compromised
hand-held shutter speeds with my P&S cameras. I can shoot my FZ50 at ISO
100 with IS at 420mm EFL in a shady street and get tack-sharp pictures of
relatively stationary objects, with shutter speeds sometimes down to 1/30.
With my 30D, I'd have to use ISO 800 to 1600 with my 300mm IS, and get
about 1 - 1.6 stops stronger read noise in the shadows.

The slappin' mirror has got to go the way of the dinosaurs. It is
primitive BS.

--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <(E-Mail Removed)>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

 
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dj_nme
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      07-06-2008
Alfred Molon wrote:
> In article <Xns9AD171A83C2E4jpsnokomm@130.81.64.196>, John Sheehy
> says...
>
>> The slappin' mirror has got to go the way of the dinosaurs. It is
>> primitive BS.

>
> And the cameras should use the main sensor for metering (most DLSRs with
> live preview don't do that). The only problem is that to have phase AF
> you need a mirror.


Phase detection AF requires the image to be reflected onto the sensors,
not necessarily by a single large reflex mirror, as for the viewfinder.
In fact, I'm sure that Phase detection sensors have their own smaller
mirrors which are normally hidden behind the viewfinder reflex mirror.
As far as I'm aware, Phase detection AF has not been implemented in
anything other than SLR cameras.

It should be possible to have a non-slr stills camera with their smaller
mirrors flipping out of the way when the shutter is tripped and because
of their smaller mass shouldn't cause mirror-slap shake.
Something like a RF camera could have an AF mode that uses Phase
detection, but the handful of current RF camera makers (Leica, Cosina,
any-one else?) only have manual focus.

Video would be another problem, as the mirrors for the AF sensors would
have to be out of the way the whole time.
I suppose you could side-step the need for moving mirrors with a
pellicle style mirror for the AF sensors, at least that way there is no
slap and the Phase detection AF sensors could also be used in stills mode.
The downside would be losing at least a stop of brightness going to the
imaging sensor.
 
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David J Taylor
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      07-06-2008
Alfred Molon wrote:
[]
> And the cameras should use the main sensor for metering (most DLSRs
> with live preview don't do that).

[]


Why, when separate metering sensor can have a much greater dynamic range?

David


 
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David J Taylor
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      07-06-2008
Alfred Molon wrote:
> In article <J7Zbk.21480$(E-Mail Removed)> , David J
> Taylor says...
>> Alfred Molon wrote:
>> []
>>> And the cameras should use the main sensor for metering (most DLSRs
>>> with live preview don't do that).

>> []
>>
>>
>> Why, when separate metering sensor can have a much greater dynamic
>> range?

>
> Because separate metering sensors are not that precise (there are too
> few of them), forcing the camera to be very conservative in setting
> the exposure, which often leads to underexposures.
>
> Not sure why greater dynamic range than the sensor can capture would
> be an advantage, since the sensor can't capture it anyway.


Alfred,

I might argue that there's no "correct" exposure, and taking an average
over a few pixels (because of lack of area precision) is no worse than
taking pixel-sized values, but I take your point.

As to dynamic range, wouldn't you want a meter which had greater range
than the sensor? Otherwise at the high end you just get: "It's over the
limit" rather than it's 5% over the limit or it's 100% over the limit. I
was also thinking that larger pixels in the exposure sensor might lead to
greater precision (in the shadows) than inherently noisier (because they
are smaller) sensor pixels.

Cheers,
David


 
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Ray Fischer
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      07-06-2008
Alfred Molon <(E-Mail Removed)> wrote:
> David J Taylor says...
>> Alfred Molon wrote:


>> > And the cameras should use the main sensor for metering (most DLSRs
>> > with live preview don't do that).

>>
>> Why, when separate metering sensor can have a much greater dynamic range?

>
>Because separate metering sensors are not that precise (there are too
>few of them), forcing the camera to be very conservative in setting the
>exposure, which often leads to underexposures.
>
>Not sure why greater dynamic range than the sensor can capture would be
>an advantage, since the sensor can't capture it anyway.


Because the sensor CAN capture it given an appropriate exposure. The
metering sensor doesn't have the luxury of being able to adjust
shutter speed or diaphram to meter light levels from bright sunlight
to near darkness.

And no, adjusting the lens diaphram is not an option. It'd suck
power, wear down the lens, possibly burn out the diaphram motor,
and wouldn't even work for lenses that do not have camera-controlled
diaphrams.

--
Ray Fischer
http://www.velocityreviews.com/forums/(E-Mail Removed)

 
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ASAAR
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      07-06-2008
On Fri, 04 Jul 2008 15:10:09 GMT, John Sheehy wrote:

> I can shoot my FZ50 at ISO
> 100 with IS at 420mm EFL in a shady street and get tack-sharp pictures of
> relatively stationary objects, with shutter speeds sometimes down to 1/30.


The operative word being "sometimes". The keeper rate would
probably be fairly low, and even those probably could only be called
"tack-sharp" using a very loose interpretation. Other than the few
that wear a cape and have a large "S" on their chest, most people
will see a tremendous increase in the sharpness of their shots when
going from 1/30th sec to using a tripod with a 420mm EFL lens.


> With my 30D, I'd have to use ISO 800 to 1600 with my 300mm IS, and get
> about 1 - 1.6 stops stronger read noise in the shadows.


Please. If you needed to use ISO 800 with a 30D hobbled by
mirror-slap to remain competitive with your P&S, then you forgot to
turn on the 300mm's IS. I'll bet this whole exercise was to give
you the opportunity to once again talk up your P&S's low read noise.


> The slappin' mirror has got to go the way of the dinosaurs. It is
> primitive BS.


Agreed. There's much too much BS going around these days.

 
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Ray Fischer
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      07-07-2008
Alfred Molon <(E-Mail Removed)> wrote:
> Ray Fischer


>> And no, adjusting the lens diaphram is not an option. It'd suck
>> power, wear down the lens, possibly burn out the diaphram motor,
>> and wouldn't even work for lenses that do not have camera-controlled
>> diaphrams.

>
>Non-DLSRs use this diaphragm technique without any of the problems you
>mention.


Then buy a P&S and suffer with its shortcomings. There's a reason the
dSLRs are faster.

--
Ray Fischer
(E-Mail Removed)

 
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