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Meaning of ISO value in digital photography?



 
 
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  #11  
Old June 15th 18, 03:26 AM posted to rec.photo.digital
Ken Hart[_4_]
external usenet poster
 
Posts: 569
Default Meaning of ISO value in digital photography?

On 06/14/2018 03:29 PM, Savageduck wrote:
On Jun 14, 2018, Jim-P wrote
(in et):

In film cameras, ISO referrs to the sensitivity to light of the emulsion.
Manufacturers formulate different film emulsions with different
sensitivites tarding increased grain with increased ISO speed.


Correct. The important thing is not to conflate analog ISO ratings with
digital ratings. They are two different things.

In a digital camera, presumably the sensor does not adjust itself to have
greater sensitivity. Or does it?


Any given sensor will have a base sensitivety, or ISO. Typically ISO 200, or
ISO 100 depending on manufacturer.


Really? I've never looked into that, but I would have thought that the
base sensitivity would be closer to the mid-point of the camera's ISO
setting range. But that's just electronics design practice.

The sensitivety does not change in the
same way that analog film emulsions can be changed. Any increase from the
base ISO is an increase of signal gain, or amplification of the signal from
the sensor.

So what is happening in a digital camera when I choose a greater ISO
setting? Is more amplification being used?


What you are doing when increasing the ISO number with a digital camera is
increasing the signal gain between the sensor and the camera CPU. This is
effectively the same as turning up the volume (gain) on an audio amplifier.
As gain increases so does amplified noise. How the noise manifests itself
depends on the sensor, the CPU, and the SNR of the pair. That is why some
cameras have better high ISO performance than others.

By using ISO to rate the base sensor sensitivity, and any increases by upping
the gain just gives folks who have made the move from film to digital a rough
guide by referencing film ISO.

I tried to understand this page but it got far too technical....

https://photography.tutsplus.com/art...n--photo-11963


That article is spelling out the fact that digital ISO is not the equivalent
of analoge ISO.


That article does have a high nerd factor. Generally when an article
emphasizes that we are using log-10 not log-e, you need a couple letters
after your name!



--
Ken Hart

  #12  
Old June 15th 18, 03:47 AM posted to rec.photo.digital
Savageduck[_3_]
external usenet poster
 
Posts: 16,487
Default Meaning of ISO value in digital photography?

On Jun 14, 2018, Ken Hart wrote
(in article ):

On 06/14/2018 08:05 PM, Savageduck wrote:
On Jun 14, 2018, Jim-P wrote
(in article ):

On Thu, 14 Jun 2018 14:26:40 -0400, PeterN wrote:

On 6/14/2018 1:48 PM, Jim-P wrote:
In film cameras, ISO referrs to the sensitivity to light of the emulsion.
Manufacturers formulate different film emulsions with different
sensitivites tarding increased grain with increased ISO speed.

In a digital camera, presumably the sensor does not adjust itself to have
greater sensitivity. Or does it?

So what is happening in a digital camera when I choose a greater ISO
setting? Is more amplification being used?

I tried to understand this page but it got far too technical....

https://photography.tutsplus.com/art...n--photo-11963

I am going to try to give you a simplified, non-technical explanation.
As with most generalities it is not 100% technically accurate, but
should serve as a guideline.
ISO is a measurement of the light sensitivity of the sensor. Digital ISO
is adjustable in many cameras. And yes, it is a matter of adjusting the
amplification. If you are using a wider lens opening, and slower shutter
speed, you will be able to use a lower ISO.
Digital noise is one of the undesired artifacts in the image. Higher ISO
will result in more digital noise, and lessor image quality. Many of the
newer high quality sensors are designed to work at a higher ISO, with
less noticeable noise, and reduction in image quality.
There are some of us here who do not object to noise, while others have
serious objections. The point at which noise becomes objectionable often
comes down to a matter of taste and personal preferences.

Thanks. This makes me wonder what ISO I should set, if I don't leave it on
auto.


In the film days, we used the "Sunny-16" rule: Set the shutter speed
equal to the ISO (then "ASA"). In bright sunshine, use f/16. Slightly
cloudy- use f/11, open shade- f/8, full shade- f/5.6. This technique
would usually give a good exposure.

Combine that with the "focal length equals shutter speed" rule: The
longer the focal length, the faster the shutter speed to give acceptable
hand-held images. For a 200mm lens, you use a shutter speed of 1/250
second.

Example: 100mm lens calls for 1/100 second minimum. Set the ISO also at
100, and use the "Sunny-16" rule. Then refer to SD's exposure triangle,
three paragraphs down...

Let us start by asking, what camera are you using?


It would still be good to know what camera the OP is using.

As far as which ISO you should use you should consider the light environment
of the scene you are trying to capture, along with your interpretation of
that scene, all balanced to achieve an acceptable exposure.

Auto ISO can work, but you are going to be better off if you have an
understanding of the exposure triangle and photography in general. It might
be time for you to read a book on photography.


f/stop, shutter speed, and ISO.


That is where we all should start.

With a higher ISO, you can use a faster shutter speed and smaller lens
aperture. You get better motion stopping and depth of field, but you
also get grain (or noise).
With a lower ISO, you need to either use a slower shutter speed or a
wider aperture. You get better "grain", but you lose motion-stopping or
depth of field.
It's all a trade-off.


That is the story in a nutshell.


Does ISO 200 on a digital camera broadly match the grain/noise of ISO 200
Fujicolor or Kodacolor that I used to use years ago?


Close enough.


I'm going to have to respectfully disagree with SD here, but just on his
two word paragraph.


Well, I guess my two word paragraph was an over simplification for a
photographer new to digital photography. My “close enough” should have
been qualified as relative to the camera being used, and we have yet to
assertain what the OP is using. In my case I am using APS-C Nikon, and
Fujifilm cameras.

The "grain" of a digital sensor would be relative to the pixel count of
that sensor. To go to the extreme, a 3K-pixel toy camera would have a
"grainy" image no matter how low you dial the ISO- assuming that such a
camera would have that feature! OTOH, a 48M-pixel medium format digital
back would have a very tight "grain" pattern, exceeding that of 35mm ISO
200 film.


What the digital sensor produces is noise, and to call it “grain” is
wishful thinking. At higher digital ISO settings, or increased gain noise
becomes more apparant. The amount of noise depends on the sensor (size, and
vintage) and CPU camera manufacturer. These days it is not necessary to go to
a large MF format sensor to exceed the performance of 35mm ISO 200 film.
There are APS-C cameras such as the D500, X-T2, and X-H1which can do that
without much effort.

However, there are some software emulations which are capable producing very
good emulations of analog film grain which appear to be grain, not noise. Two
of the best at doing this are NIK Silver Efex Pro2, and Alien Skin Exposure
X3. Then Fujifilm has very good in-camera film emulations which produce
excellent results with three levels of simulated film like grain production.

Or do the ISO settings for a digital camera give quite different results to
the ISO values of film?


In a digital camera the ISO settings are going to be a close approximation
of ISO values of film, and are more guidelines rather than exact figures.


In fact, there will _some_ variation in the ISO between manufacturers of
film, and the emulsion batches. Which is why many pros would buy large
quantities of film, and shoot a few test rolls before shooting work for
pay.


....and some of those pros still have rolls of film in refrigerated storage.


For example, you are going to find it difficult to dig up ISO 51200 film, but
there are digital cameras capable of producing acceptable images with ISO
that high.


--

Regards,
Savageduck

  #13  
Old June 15th 18, 04:04 AM posted to rec.photo.digital
nospam
external usenet poster
 
Posts: 24,165
Default Meaning of ISO value in digital photography?

In article , Ken Hart
wrote:

Does ISO 200 on a digital camera broadly match the grain/noise of ISO 200
Fujicolor or Kodacolor that I used to use years ago?


Close enough.


I'm going to have to respectfully disagree with SD here, but just on his
two word paragraph.

The "grain" of a digital sensor would be relative to the pixel count of
that sensor. To go to the extreme, a 3K-pixel toy camera would have a
"grainy" image no matter how low you dial the ISO- assuming that such a
camera would have that feature! OTOH, a 48M-pixel medium format digital
back would have a very tight "grain" pattern, exceeding that of 35mm ISO
200 film.


false.

you're confusing 'grain', or digital noise, with resolution.

a 3 kp camera has a lower *resolution* than a 48 mp camera.

noise depends on the pixel size, or how much light is collected. larger
pixels have less noise.

sd is correct in that iso 200 on a digital camera is equivalent to iso
200 on a film camera with regards to exposure. it won't necessarily be
*exactly* the same, but as he said 'close enough'.

however, sd is not correct in that the grain/noise will be close.

for digital, the noise will be *significantly* less than film grain at
the same iso. it's nowhere near close.

nikon d850 at iso 3200 & 25600:
https://i.ytimg.com/vi/5k92LnEGOKo/maxresdefault.jpg

nikon d810/d850/d500 at iso 12800:
https://i.ytimg.com/vi/y_kk7QhS-MU/maxresdefault.jpg

being able to shoot at iso 3200-6400 and beyond without worrying about
noise opens up a whole new world not possible with film.
  #14  
Old June 15th 18, 04:04 AM posted to rec.photo.digital
nospam
external usenet poster
 
Posts: 24,165
Default Meaning of ISO value in digital photography?

In article , Ken Hart
wrote:


In a digital camera, presumably the sensor does not adjust itself to have
greater sensitivity. Or does it?


Any given sensor will have a base sensitivety, or ISO. Typically ISO 200, or
ISO 100 depending on manufacturer.


Really?


really.

I've never looked into that, but I would have thought that the
base sensitivity would be closer to the mid-point of the camera's ISO
setting range. But that's just electronics design practice.


actually, it isn't.

I tried to understand this page but it got far too technical....


https://photography.tutsplus.com/art...ical-explorati
on--photo-11963


That article is spelling out the fact that digital ISO is not the equivalent
of analoge ISO.


That article does have a high nerd factor. Generally when an article
emphasizes that we are using log-10 not log-e, you need a couple letters
after your name!


the fact that the article is talking about p-n junctions and reverse
biasing diodes indicates that its intended target audience are
electrical engineers, not ordinary photographers.
  #15  
Old June 15th 18, 04:10 AM posted to rec.photo.digital
Savageduck[_3_]
external usenet poster
 
Posts: 16,487
Default Meaning of ISO value in digital photography?

On Jun 14, 2018, Ken Hart wrote
(in article ):

On 06/14/2018 03:29 PM, Savageduck wrote:


Snip

Any given sensor will have a base sensitivety, or ISO. Typically ISO 200, or
ISO 100 depending on manufacturer.


Really? I've never looked into that, but I would have thought that the
base sensitivity would be closer to the mid-point of the camera's ISO
setting range. But that's just electronics design practice.


Yup!

Take the Nikon D800 which has a base of ISO 100, and the D810 which has been
reduced to ISO 64. Any increase in ISO is an increase of signal gain from the
sensor. Both of those cameras are capable of dealing with very high ISO
settings without producing noticeable noise.

In the APS-C world the D500 has a base of ISO 100, and can be cranked up to
ISO 51,200, and extended to an unthinkable ISO 1,640,000.

My APS-C Fujifilm X-T2 on the other hand can shoot from a base ISO 200 to ISO
12800, and can be extended down to ISO 160, 125, & 100, or up to ISO 25,600,
and ISO 51,200.

These are worth a read:

https://www.bhphotovideo.com/explora...aphy/tips-and-
solutions/understanding-exposure-part-4-iso

https://www.jmpeltier.com/2018/02/13/what-is-extended-iso-native-iso/

This one is a real simplification:

https://photographylife.com/what-is-iso-in-photography
--

Regards,
Savageduck

  #16  
Old June 15th 18, 05:16 AM posted to rec.photo.digital
PeterN[_7_]
external usenet poster
 
Posts: 1,161
Default Meaning of ISO value in digital photography?

On 6/14/2018 10:26 PM, Ken Hart wrote:
On 06/14/2018 03:29 PM, Savageduck wrote:
On Jun 14, 2018, Jim-P wrote
(in et):

In film cameras, ISO referrs to the sensitivity to light of the
emulsion.
Manufacturers formulate different film emulsions with different
sensitivites tarding increased grain with increased ISO speed.


Correct. The important thing is not to conflate analog ISO ratings with
digital ratings. They are two different things.

In a digital camera, presumably the sensor does not adjust itself to
have
greater sensitivity. Or does it?


Any given sensor will have a base sensitivety, or ISO. Typically ISO
200, or
ISO 100 depending on manufacturer.


Really? I've never looked into that, but I would have thought that the
base sensitivity would be closer to the mid-point of the camera's ISO
setting range. But that's just electronics design practice.

The sensitivety does not change in the
same way that analog film emulsions can be changed. Any increase from the
base ISO is an increase of signal gain, or amplification of the signal
from
the sensor.

So what is happening in a digital camera when I choose a greater ISO
setting? Is more amplification being used?


What you are doing when increasing the ISO number with a digital
camera is
increasing the signal gain between the sensor and the camera CPU. This is
effectively the same as turning up the volume (gain) on an audio
amplifier.
As gain increases so does amplified noise. How the noise manifests itself
depends on the sensor, the CPU, and the SNR of the pair. That is why some
cameras have better high ISO performance than others.

By using ISO to rate the base sensor sensitivity, and any increases by
upping
the gain just gives folks who have made the move from film to digital
a rough
guide by referencing film ISO.

I tried to understand this page but it got far too technical....

https://photography.tutsplus.com/art...n--photo-11963


That article is spelling out the fact that digital ISO is not the
equivalent
of analoge ISO.


That article does have a high nerd factor. Generally when an article
emphasizes that we are using log-10 not log-e, you need a couple letters
after your name!


Both you and the Duck are correct. It all boils down to what type of
image the photographer is looking to make. I use auto ISO when I want to
use a fixed shutter speed, and a fixed aperture. As for setting an upper
limit, there are times when a really noisy image is preferable to no
image at all. I would very much prefer a very noisy and grainy image of
the abominable snow man, to no image at all.


--
PeterN
  #17  
Old June 15th 18, 08:00 PM posted to rec.photo.digital
John McWilliams
external usenet poster
 
Posts: 6,945
Default Meaning of ISO value in digital photography?

On 6/14/18 PDT 9:16 PM, PeterN wrote:
On 6/14/2018 10:26 PM, Ken Hart wrote:


Both you and the Duck are correct. It all boils down to what type of
image the photographer is looking to make. I use auto ISO when I want to
use a fixed shutter speed, and a fixed aperture. As for setting an upper
limit, there are times when a really noisy image is preferable to no
image at all. I would very much prefer a very noisy and grainy image of
the abominable snow man, to no image at all.


I've set my Canons to ISO 200 and keep it there* as I want the feedback
from aperture or shutter speed telling me when I am on the edge of
insufficient light.

* There are some exceptions!
  #18  
Old June 15th 18, 09:18 PM posted to rec.photo.digital
Jim-P
external usenet poster
 
Posts: 34
Default Meaning of ISO value in digital photography?

On Thu, 14 Jun 2018 19:47:36 -0700, Savageduck wrote:

On Jun 14, 2018, Ken Hart wrote
(in article ):

On 06/14/2018 08:05 PM, Savageduck wrote:
On Jun 14, 2018, Jim-P wrote
(in article ):

On Thu, 14 Jun 2018 14:26:40 -0400, PeterN wrote:

On 6/14/2018 1:48 PM, Jim-P wrote:
In film cameras, ISO referrs to the sensitivity to light of the emulsion.
Manufacturers formulate different film emulsions with different
sensitivites tarding increased grain with increased ISO speed.

In a digital camera, presumably the sensor does not adjust itself to have
greater sensitivity. Or does it?

So what is happening in a digital camera when I choose a greater ISO
setting? Is more amplification being used?

I tried to understand this page but it got far too technical....

https://photography.tutsplus.com/art...n--photo-11963

I am going to try to give you a simplified, non-technical explanation.
As with most generalities it is not 100% technically accurate, but
should serve as a guideline.
ISO is a measurement of the light sensitivity of the sensor. Digital ISO
is adjustable in many cameras. And yes, it is a matter of adjusting the
amplification. If you are using a wider lens opening, and slower shutter
speed, you will be able to use a lower ISO.
Digital noise is one of the undesired artifacts in the image. Higher ISO
will result in more digital noise, and lessor image quality. Many of the
newer high quality sensors are designed to work at a higher ISO, with
less noticeable noise, and reduction in image quality.
There are some of us here who do not object to noise, while others have
serious objections. The point at which noise becomes objectionable often
comes down to a matter of taste and personal preferences.

Thanks. This makes me wonder what ISO I should set, if I don't leave it on
auto.


In the film days, we used the "Sunny-16" rule: Set the shutter speed
equal to the ISO (then "ASA"). In bright sunshine, use f/16. Slightly
cloudy- use f/11, open shade- f/8, full shade- f/5.6. This technique
would usually give a good exposure.

Combine that with the "focal length equals shutter speed" rule: The
longer the focal length, the faster the shutter speed to give acceptable
hand-held images. For a 200mm lens, you use a shutter speed of 1/250
second.

Example: 100mm lens calls for 1/100 second minimum. Set the ISO also at
100, and use the "Sunny-16" rule. Then refer to SD's exposure triangle,
three paragraphs down...

Let us start by asking, what camera are you using?


It would still be good to know what camera the OP is using.


I am using a smartphone camera. Although it is not as high quality as a
DSLR the principles should be the same and I am interested in understanding
them before taking my photography further.

The smartphone model is a Moto G5 Plus with a Sony IMX362 Exmor RS camera
module which is also used in the Nokia 7 and Samsung S7 Edge

https://phoneproscons.com/794/moto-g...enfone-3-zoom/

I recall that old Sunny 16 rule and the thing which strikes me most about
it now is how slow the shutter speeds were in the old days. 1/250 was one
of the faster speeds I would use for day to day photography years ago but
my current smartphone often uses speeds of 1/1000 or 1/2000 which is
fantastic because by hand steadiness is not what it used to be.
  #19  
Old June 15th 18, 09:32 PM posted to rec.photo.digital
Savageduck[_3_]
external usenet poster
 
Posts: 16,487
Default Meaning of ISO value in digital photography?

On Jun 15, 2018, John McWilliams wrote
(in article ):

On 6/14/18 PDT 9:16 PM, PeterN wrote:
On 6/14/2018 10:26 PM, Ken Hart wrote:


Both you and the Duck are correct. It all boils down to what type of
image the photographer is looking to make. I use auto ISO when I want to
use a fixed shutter speed, and a fixed aperture. As for setting an upper
limit, there are times when a really noisy image is preferable to no
image at all. I would very much prefer a very noisy and grainy image of
the abominable snow man, to no image at all.

I've set my Canons to ISO 200 and keep it there* as I want the feedback
from aperture or shutter speed telling me when I am on the edge of
insufficient light.

* There are some exceptions!


I believe that there are going to be quite a number of exceptions. ;-)

--

Regards,
Savageduck

  #20  
Old June 15th 18, 09:46 PM posted to rec.photo.digital
Savageduck[_3_]
external usenet poster
 
Posts: 16,487
Default Meaning of ISO value in digital photography?

On Jun 15, 2018, Jim-P wrote
(in article ):

On Thu, 14 Jun 2018 19:47:36 -0700, Savageduck wrote:

On Jun 14, 2018, Ken Hart wrote
(in article ):

On 06/14/2018 08:05 PM, Savageduck wrote:
On Jun 14, 2018, Jim-P wrote
(in article ):

On Thu, 14 Jun 2018 14:26:40 -0400, PeterN wrote:

On 6/14/2018 1:48 PM, Jim-P wrote:
In film cameras, ISO referrs to the sensitivity to light of the
emulsion.
Manufacturers formulate different film emulsions with different
sensitivites tarding increased grain with increased ISO speed.

In a digital camera, presumably the sensor does not adjust itself to
have
greater sensitivity. Or does it?

So what is happening in a digital camera when I choose a greater ISO
setting? Is more amplification being used?

I tried to understand this page but it got far too technical....

https://photography.tutsplus.com/art...echnical-explo
ration--photo-11963

I am going to try to give you a simplified, non-technical explanation.
As with most generalities it is not 100% technically accurate, but
should serve as a guideline.
ISO is a measurement of the light sensitivity of the sensor. Digital ISO
is adjustable in many cameras. And yes, it is a matter of adjusting the
amplification. If you are using a wider lens opening, and slower shutter
speed, you will be able to use a lower ISO.
Digital noise is one of the undesired artifacts in the image. Higher ISO
will result in more digital noise, and lessor image quality. Many of the
newer high quality sensors are designed to work at a higher ISO, with
less noticeable noise, and reduction in image quality.
There are some of us here who do not object to noise, while others have
serious objections. The point at which noise becomes objectionable often
comes down to a matter of taste and personal preferences.

Thanks. This makes me wonder what ISO I should set, if I don't leave it
on
auto.

In the film days, we used the "Sunny-16" rule: Set the shutter speed
equal to the ISO (then "ASA"). In bright sunshine, use f/16. Slightly
cloudy- use f/11, open shade- f/8, full shade- f/5.6. This technique
would usually give a good exposure.

Combine that with the "focal length equals shutter speed" rule: The
longer the focal length, the faster the shutter speed to give acceptable
hand-held images. For a 200mm lens, you use a shutter speed of 1/250
second.

Example: 100mm lens calls for 1/100 second minimum. Set the ISO also at
100, and use the "Sunny-16" rule. Then refer to SD's exposure triangle,
three paragraphs down...

Let us start by asking, what camera are you using?


It would still be good to know what camera the OP is using.


I am using a smartphone camera. Although it is not as high quality as a
DSLR the principles should be the same and I am interested in understanding
them before taking my photography further.

The smartphone model is a Moto G5 Plus with a Sony IMX362 Exmor RS camera
module which is also used in the Nokia 7 and Samsung S7 Edge

https://phoneproscons.com/794/moto-g...camera-same-am
azing-sensor-as-in-xplay-6-and-zenfone-3-zoom/


There is nothing wrong in using a smartphone camera. However, you are going
to have limitations which you will not find in modern DSLR, or mirrorless
digital cameras (MILC). Even with third party photo apps for your smartphone
you are going to have limitations of physical sensor size, and adjustability
of the exposure triangle.

The next question is; are you intending to add a modern digital camera to
your current photography kit?

I recall that old Sunny 16 rule and the thing which strikes me most about
it now is how slow the shutter speeds were in the old days. 1/250 was one
of the faster speeds I would use for day to day photography years ago but
my current smartphone often uses speeds of 1/1000 or 1/2000 which is
fantastic because by hand steadiness is not what it used to be.


True. However, that was in the days of 25 ASA film. Things have changed,
along with high ISO performance with fast lenses, there are other technical
improvements with things such as various types of image stabilization with
stabilized lenses (VR, IS, OIS), and in camera image stabilization (IBIS).

--

Regards,
Savageduck

 




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