# ISO question

Discussion in 'Digital Photography' started by Ockham's Razor, Apr 12, 2007.

1. ### Ockham's RazorGuest

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?

--
"When fascism comes to America, it will be wrapped in the flag and
carrying a cross."
Sinclair Lewis

Ockham's Razor, Apr 12, 2007

2. ### JimGuest

"Ockham's Razor" <> wrote in message
news:-sjc.supernews.net...
> 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?
>
> --
> "When fascism comes to America, it will be wrapped in the flag and
> carrying a cross."
> Sinclair Lewis

A camera is a camera is a camera....

Figure it out for yourself. The exposure time is:

T = N*N/(S * B)
Where T = shutter speed in seconds
N = focal ratio (i. e. f stop)
S = ISO speed
B = Bightness of illumination in candelas per square foot.

You will find this equation lots of places. A couple are Michael
Covington's bool "Astrophotograpy for Amateurs" and Rudolf Kingslake's book
"Lenses in Photography".
Kingslake's book is long out of print.

Note: A candela is merely a closely specified version of a candle. If you
search the internet for "candela", you will find more information than you
ever imagined.

Jim

Jim, Apr 12, 2007

3. ### MarvinGuest

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

Marvin, Apr 12, 2007
4. ### Matt IonGuest

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/8). 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.

Matt Ion, Apr 12, 2007
5. ### M-MGuest

In article <sBuTh.64610\$6m4.5332@pd7urf1no>,
Matt Ion <> 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.

--
m-m

M-M, Apr 12, 2007
6. ### Ed RufGuest

On Thu, 12 Apr 2007 14:17:06 -0400, in rec.photo.digital M-M
<> wrote:

>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 is the focal length of the specific lens you are considering. So
consider the 70or 80-200mm f/2.8 lenses. The max aperture of the lens
is then 200mm / 2.8 = 71.4mm.
-
Ed Ruf ()
http://edwardgruf.com/Digital_Photography/General/index.html

Ed Ruf, Apr 12, 2007
7. ### Ken LuckeGuest

In article <>, M-M
<> wrote:

> In article <sBuTh.64610\$6m4.5332@pd7urf1no>,
> Matt Ion <> 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

Ken Lucke, Apr 12, 2007
8. ### David Dyer-BennetGuest

M-M wrote:
> In article <sBuTh.64610\$6m4.5332@pd7urf1no>,
> Matt Ion <> 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

David Dyer-Bennet, Apr 12, 2007
9. ### WestyGuest

On Thu, 12 Apr 2007 07:58:34 -0700, 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?

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?

Westy, Apr 12, 2007
10. ### Bill FunkGuest

On Thu, 12 Apr 2007 13:20:56 -0400, Marvin <>
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

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.

Bill Funk, Apr 12, 2007
11. ### Bill FunkGuest

On Thu, 12 Apr 2007 14:17:06 -0400, M-M <> wrote:

>In article <sBuTh.64610\$6m4.5332@pd7urf1no>,
> Matt Ion <> 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.

Bill Funk, Apr 12, 2007
12. ### John SheehyGuest

Ockham's Razor <> wrote in news:Mencken-
-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 <>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

John Sheehy, Apr 12, 2007
13. ### MarvinGuest

Bill Funk wrote:
> On Thu, 12 Apr 2007 13:20:56 -0400, Marvin <>
> 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

>
> 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.

Marvin, Apr 13, 2007
14. ### Bill FunkGuest

On Fri, 13 Apr 2007 15:27:17 -0400, Marvin <>
wrote:

>Bill Funk wrote:
>> On Thu, 12 Apr 2007 13:20:56 -0400, Marvin <>
>> 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

>>
>> 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
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.

Bill Funk, Apr 14, 2007
15. ### MarvinGuest

Bill Funk wrote:
> On Fri, 13 Apr 2007 15:27:17 -0400, Marvin <>
> wrote:
>
>> Bill Funk wrote:
>>> On Thu, 12 Apr 2007 13:20:56 -0400, Marvin <>
>>> 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
>>> 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.

Marvin, Apr 14, 2007
16. ### David Dyer-BennetGuest

Marvin wrote:

> 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.

But it shows new shadow detail, which pushing film doesn't.

David Dyer-Bennet, Apr 14, 2007
17. ### MarvinGuest

David Dyer-Bennet wrote:
> Marvin wrote:
>
>> 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.

>
> But it shows new shadow detail, which pushing film doesn't.

The comparison is not literal. Film and digital are
different technologies, and it one should understand the
differences to get the most of either one. What I initially
wrote on this subject was meant to help readers who haven't
yet learned the details. This following discussion is
interesting for those who do know at least some of the details.

Marvin, Apr 15, 2007
18. ### Bill FunkGuest

On Sat, 14 Apr 2007 16:02:40 -0400, Marvin <>
wrote:

>Bill Funk wrote:
>> On Fri, 13 Apr 2007 15:27:17 -0400, Marvin <>
>> wrote:
>>
>>> Bill Funk wrote:
>>>> On Thu, 12 Apr 2007 13:20:56 -0400, Marvin <>
>>>> 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
>>>> 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.

In a digital camera, the adjustment is done by adjusting the exposure
directly during the shot, unlike pushing, which is done *after* the
pic is shot.
>
>> '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.

No, I'm not aware of that.
And even after a Google search, I'm still not.
If I get what you're saying, then you're saying all brightness
brightness will affect the overall contrast.
Gamma, OTOH, is different from contrast; it controls the overall
brightness of an image, especially as seen on a monitor. Changing the
gamma not only controls brightness, but also the ratios of green to
blue to red.

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

The White House admitted on Wednesday that
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.

Bill Funk, Apr 15, 2007
19. ### MarvinGuest

Bill Funk wrote:
> On Sat, 14 Apr 2007 16:02:40 -0400, Marvin <>
> wrote:

> No, I'm not aware of that.
> And even after a Google search, I'm still not.
> If I get what you're saying, then you're saying all brightness
> brightness will affect the overall contrast.
> Gamma, OTOH, is different from contrast; it controls the overall
> brightness of an image, especially as seen on a monitor. Changing the
> gamma not only controls brightness, but also the ratios of green to
> blue to red.
>

You still don't understand what gamma means. Here is a link
http://www.dpreview.com/learn/?/Glossary/Digital_Imaging/Gamma_01.htm

Marvin, Apr 16, 2007
20. ### Bill FunkGuest

On Mon, 16 Apr 2007 11:36:45 -0400, Marvin <>
wrote:

>Bill Funk wrote:
>> On Sat, 14 Apr 2007 16:02:40 -0400, Marvin <>
>> wrote:

>
>> No, I'm not aware of that.
>> And even after a Google search, I'm still not.
>> If I get what you're saying, then you're saying all brightness
>> brightness will affect the overall contrast.
>> Gamma, OTOH, is different from contrast; it controls the overall
>> brightness of an image, especially as seen on a monitor. Changing the
>> gamma not only controls brightness, but also the ratios of green to
>> blue to red.
>>

>
>You still don't understand what gamma means. Here is a link
>http://www.dpreview.com/learn/?/Glossary/Digital_Imaging/Gamma_01.htm

This does not say Gamma is about contrast.
In fact, it seems to be saying what I said; Gamma is about the
brightness of the image, especiually ass een on a monitor.
Taking a washed-out image, and adjusting Gamma will make it look more
contrasy, but you do it by adjusting brightness, not contrast.

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

Hillary Clinton told New Hampshire voters
Sunday that President Bush's refusal to change
course in Iraq is a tragedy of historic proportion.
That's fine with her. The more unforgivable the
president, the more Hillary Clinton seems to get
out of it.

Bill Funk, Apr 17, 2007