ISO question

Ockham's Razor wrote:
> Does increasing the ISO setting on a digital camera do the same thing as
> opening the shutter? If so, is there any info on the shutter stop
> equivalent for a given increase in ISO?
>
In digicams, the ISO setting does not affect the exposure
settings. It changes the amplification (i.e., gain) in
reading the image pixels.
 >> Stay informed about: ISO question 

On Thu, 12 Apr 2007 13:20:56 -0400, Marvin <physchem.RemoveThis@cloud9.net>
wrote:

>Ockham's Razor wrote:
>> Does increasing the ISO setting on a digital camera do the same thing as
>> opening the shutter? If so, is there any info on the shutter stop
>> equivalent for a given increase in ISO?
>>
>In digicams, the ISO setting does not affect the exposure
>settings. It changes the amplification (i.e., gain) in
>reading the image pixels.

Well, it *should* affect the exposure.
Doubling the ISO means half the light is needed for proper exposure.
Thus, if proper exposure at ISO 100 is f/4 @ 1/100 sec shutter speed,
doubling the ISO to 200 would let you go up one f/stop or halve the
shutter speed (or a proper combination of the two).

--
THIS IS A SIG LINE; NOT TO BE TAKEN SERIOUSLY!

Hillary Clinton visited a veteran's hospital
in Syracuse Tuesday and promised better care
for wounded veterans. She's wounded her share.
Whenever the Commander-in-Chief used to walk
into the Rose Garden with a black eye, you
knew he was having a good week.
 >> Stay informed about: ISO question 

Ockham's Razor wrote:
> Does increasing the ISO setting on a digital camera do the same thing as
> opening the shutter? If so, is there any info on the shutter stop
> equivalent for a given increase in ISO?

The ISO setting in digital cameras affects how sensitive the camera is to light
(or more technically, it adjusts how much the signal from the sensor is
boosted). It's intended to correspond to the ISO rating of film, which is a
rating of how sensitive a film is to light (higher ISO = more sesitivity).

In both digital and film, there are always trade-offs: higher ISO means you need
less light, but you get more "noise" in the image and less contrast; wider
aperture allows more light, but reduces depth of focus; slower shutter allows
more light, but increases the chance of motion blur.

There is a direct correlation when calculating the effect of the three. Each
doubling of ISO doubles the sensitivity to light (ISO 200 to 400, for example).
One full "stop" on the aperture also means a doubling or halving of the light
allowed (f/4 passes twice as much light as f/5.6 - you'll note that every
doubling or halving of the aperture number is actually two stops of exposure,
eg. f/4 to f/. So at a given shutter speed, 200 ISO at f/4 will give the same
exposure as 400 ISO at f/5.6, as will 800 ISO at f/8, or 100 ISO at f/2.8.
 >> Stay informed about: ISO question 

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 >> Stay informed about: ISO question 

In article <nospam-C12A46.14170612042007.DeleteThis@newsread.uslec.net>, M-M
<nospam.DeleteThis@ny.more> wrote:

> In article <sBuTh.64610$6m4.5332@pd7urf1no>,
> Matt Ion <soundy106.DeleteThis@gmail.com> wrote:
>
> > So at a given shutter speed, 200 ISO at f/4 will give the same
> > exposure as 400 ISO at f/5.6, as will 800 ISO at f/8, or 100 ISO at f/2.8.
>
> That was a good explanation.
>
> But what do the aperture numbers represent? 2.8-what? Or is it
> 1/2.8-something? And what is the relationship between the numbers?
>
> I believe f/64 represents one millimeter of aperture. Is there a way to
> measure the diameter of the opening to determine the f/#?

f/# == (focal length) / (diameter of entrance pupil)

--
You need only reflect that one of the best ways to get yourself a
reputation as a dangerous citizen these days is to go about repeating
the very phrases which our founding fathers used in the struggle for
independence.
-- Charles A. Beard
 >> Stay informed about: ISO question 

M-M wrote:
> In article <sBuTh.64610$6m4.5332@pd7urf1no>,
> Matt Ion <soundy106.DeleteThis@gmail.com> wrote:
>
>> So at a given shutter speed, 200 ISO at f/4 will give the same
>> exposure as 400 ISO at f/5.6, as will 800 ISO at f/8, or 100 ISO at f/2.8.
>
> That was a good explanation.
>
> But what do the aperture numbers represent? 2.8-what? Or is it
> 1/2.8-something? And what is the relationship between the numbers?

It's a pure number, no units -- a ratio, in fact. It's the focal length
of the lens over the aperture size (in complex modern designs it's a
*bit* more complicated than that, but for the simplest case, a
single-element lens, that's accurate). That's why it's most correctly
written as f/2.8.

The "standard" sequence of f-numbers, which are all one stop apart, have
the ratio sqrt(2) between any two adjacent values, which makes sense
(given the formula for the area of a circle). There are some rounding
glitches, though .

1.4 2 2.8 4 5.6 8 11 16 22 32 45 64
 >> Stay informed about: ISO question 

On Thu, 12 Apr 2007 14:17:06 -0400, M-M <nospam.RemoveThis@ny.more> wrote:

>In article <sBuTh.64610$6m4.5332@pd7urf1no>,
> Matt Ion <soundy106.RemoveThis@gmail.com> wrote:
>
>> So at a given shutter speed, 200 ISO at f/4 will give the same
>> exposure as 400 ISO at f/5.6, as will 800 ISO at f/8, or 100 ISO at f/2.8.
>
>That was a good explanation.
>
>But what do the aperture numbers represent? 2.8-what? Or is it
>1/2.8-something? And what is the relationship between the numbers?
>
>I believe f/64 represents one millimeter of aperture. Is there a way to
>measure the diameter of the opening to determine the f/#?
>
>I've always wondered.

The best thing for you to do is get a book on basic photography; and
*read* it several times. Practice; shots with a digital camera are
free.
The inter-relationships of aperture, shutter speed and ISO are too
much to be explained in a forum such as this. Trust me on this: a book
is far better than the multitude of explanations you'll get here.


--
THIS IS A SIG LINE; NOT TO BE TAKEN SERIOUSLY!

Hillary Clinton visited a veteran's hospital
in Syracuse Tuesday and promised better care
for wounded veterans. She's wounded her share.
Whenever the Commander-in-Chief used to walk
into the Rose Garden with a black eye, you
knew he was having a good week.
 >> Stay informed about: ISO question 

This message is not archived
 >> Stay informed about: ISO question 

On Thu, 12 Apr 2007 07:58:34 -0700, Ockham's Razor <Mencken.TakeThisOut@pdx.net>
wrote:

>Does increasing the ISO setting on a digital camera do the same thing as
>opening the shutter? If so, is there any info on the shutter stop
>equivalent for a given increase in ISO?

ISO 200 is 1 stop greater than ISO100

ISO 400 is 1 stop greater than ISO200

ISO 800 is 1 stop greater than ISO400

You get the picture?
 >> Stay informed about: ISO question 

Ockham's Razor <Mencken DeleteThis @pdx.net> wrote in news:Mencken-
BA97BC.07583412042007 DeleteThis @sn-ip.vsrv-sjc.supernews.net:

> Does increasing the ISO setting on a digital camera do the same thing as
> opening the shutter?

I assume you mean opening the shutter *longer*.

Only as far as relative exposure level is concerned (exposure in the
recording format, as opposed to absolute exposure). In many ways, they are
different. The longer exposure will give more absolute exposure, and will
have less noise, relative to signal. The higher ISO will have the same
absolute exposure as the low ISO, and will have more noise, relative to
signal. I assume that all other things (f-stops) remain equal.

> If so, is there any info on the shutter stop
> equivalent for a given increase in ISO?

To get the same relative exposure, ISO and the denominator of the ex[posure
time can change proportionately. IOW, double the shutter speed, and double
the ISO, and you get the same relative exposure.

ISO 200 and 1/100, ISO 400 and 1/200, ISO 800 and 1/400 all give the same
relative exposure. ISO 800 gives the most noise. ISO 200 can give the
most motion blur.

--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS DeleteThis @no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
 >> Stay informed about: ISO question 

Bill Funk wrote:
> On Thu, 12 Apr 2007 13:20:56 -0400, Marvin <physchem.DeleteThis@cloud9.net>
> wrote:
>
>> Ockham's Razor wrote:
>>> Does increasing the ISO setting on a digital camera do the same thing as
>>> opening the shutter? If so, is there any info on the shutter stop
>>> equivalent for a given increase in ISO?
>>>
>> In digicams, the ISO setting does not affect the exposure
>> settings. It changes the amplification (i.e., gain) in
>> reading the image pixels.
>
> Well, it *should* affect the exposure.
> Doubling the ISO means half the light is needed for proper exposure.
> Thus, if proper exposure at ISO 100 is f/4 @ 1/100 sec shutter speed,
> doubling the ISO to 200 would let you go up one f/stop or halve the
> shutter speed (or a proper combination of the two).
>
I could have been more specific. In a digicam, changing the
ISO setting changes the amplification in the readout of the
image pixels. If the camera is set for automatic exposure,
it will change the the aperture setting or the exposure time
accordingly. It is analogous to how automatic exposure works
in a film camera, when a new roll of film is loaded. But in
a film camera, the ISO number refers to the sensitivity of
the film. In a digicam, a higher ISO number does not mean
that the sensor is more sensitive. Changing the readout
amplification is more like "pushing" the film development.
 >> Stay informed about: ISO question 

On Fri, 13 Apr 2007 15:27:17 -0400, Marvin <physchem.RemoveThis@cloud9.net>
wrote:

>Bill Funk wrote:
>> On Thu, 12 Apr 2007 13:20:56 -0400, Marvin <physchem.RemoveThis@cloud9.net>
>> wrote:
>>
>>> Ockham's Razor wrote:
>>>> Does increasing the ISO setting on a digital camera do the same thing as
>>>> opening the shutter? If so, is there any info on the shutter stop
>>>> equivalent for a given increase in ISO?
>>>>
>>> In digicams, the ISO setting does not affect the exposure
>>> settings. It changes the amplification (i.e., gain) in
>>> reading the image pixels.
>>
>> Well, it *should* affect the exposure.
>> Doubling the ISO means half the light is needed for proper exposure.
>> Thus, if proper exposure at ISO 100 is f/4 @ 1/100 sec shutter speed,
>> doubling the ISO to 200 would let you go up one f/stop or halve the
>> shutter speed (or a proper combination of the two).
>>
>I could have been more specific. In a digicam, changing the
>ISO setting changes the amplification in the readout of the
>image pixels. If the camera is set for automatic exposure,
>it will change the the aperture setting or the exposure time
>accordingly. It is analogous to how automatic exposure works
>in a film camera, when a new roll of film is loaded. But in
>a film camera, the ISO number refers to the sensitivity of
>the film. In a digicam, a higher ISO number does not mean
>that the sensor is more sensitive. Changing the readout
>amplification is more like "pushing" the film development.

Changing the ISO in a digital camera is the same as changing the ISO
in a film camera - the shutter speed and aperture must be changed to
correctly expose the "film".
'Pushing' in digital terms is increasing brightness or gamma in
post-processing.
That increasing the ISO in a digital camera is achieved by increasing
the amplification of the signal from the sensor is immaterial; in
effect, it is the same as increasing the ISO in film. In both digital
and film, raising the ISO requires the exposure to be adjusted to
properly expose the shot.
I don't think it really matters if the sensor is actually more
sensitive or not; the end result is the same. It's transparent to the
user. It's not analogous to pushing in film.

--
THIS IS A SIG LINE; NOT TO BE TAKEN SERIOUSLY!

The White House admitted on Wednesday that
e-mails about official business in Karl Rove's
office were erased. The deleted e-mails were
sent on Republican Party accounts instead of
White House accounts to avoid a law that
requires preservation of government records.
It doesn't clog up the landfills like Hillary's
shredder did for eight years.
 >> Stay informed about: ISO question 

Bill Funk wrote:
> On Fri, 13 Apr 2007 15:27:17 -0400, Marvin <physchem DeleteThis @cloud9.net>
> wrote:
>
>> Bill Funk wrote:
>>> On Thu, 12 Apr 2007 13:20:56 -0400, Marvin <physchem DeleteThis @cloud9.net>
>>> wrote:
>>>
>>>> Ockham's Razor wrote:
>>>>> Does increasing the ISO setting on a digital camera do the same thing as
>>>>> opening the shutter? If so, is there any info on the shutter stop
>>>>> equivalent for a given increase in ISO?
>>>>>
>>>> In digicams, the ISO setting does not affect the exposure
>>>> settings. It changes the amplification (i.e., gain) in
>>>> reading the image pixels.
>>> Well, it *should* affect the exposure.
>>> Doubling the ISO means half the light is needed for proper exposure.
>>> Thus, if proper exposure at ISO 100 is f/4 @ 1/100 sec shutter speed,
>>> doubling the ISO to 200 would let you go up one f/stop or halve the
>>> shutter speed (or a proper combination of the two).
>>>
>> I could have been more specific. In a digicam, changing the
>> ISO setting changes the amplification in the readout of the
>> image pixels. If the camera is set for automatic exposure,
>> it will change the the aperture setting or the exposure time
>> accordingly. It is analogous to how automatic exposure works
>> in a film camera, when a new roll of film is loaded. But in
>> a film camera, the ISO number refers to the sensitivity of
>> the film. In a digicam, a higher ISO number does not mean
>> that the sensor is more sensitive. Changing the readout
>> amplification is more like "pushing" the film development.
>
> Changing the ISO in a digital camera is the same as changing the ISO
> in a film camera - the shutter speed and aperture must be changed to
> correctly expose the "film".

But in a digicam, thee sensitivity of the sensor doesn't
change when the ISO is changed. The change is thta the
signal is amplified more in the readout after the exposure.
That is why I compared it to "pushing" the film in
development.

> 'Pushing' in digital terms is increasing brightness or gamma in
> post-processing.

I hope you know that gamma isn't a measure of brightness in
either film or digital photography. It has to do with contrast.
 >> Stay informed about: ISO question