How does ISO setting work?

(Ray Fischer) wrote in
:

John Sheehy wrote:

It's the lower exposure, due to the
metering for the higher ISO in auto-exposure modes, which increases
noise, relative to signal.

Inane quibbling.

It's not inane, because the common layperson's model leads to false
conclusions. In most CMOS DSLRs, higher ISOs are cleaner, in terms of what
noise the *camera* introduces into the exposure.

"Paul Furman" wrote in message
...
Neil Harrington wrote:
Most people prefer to use the lowest ISO practicable, for best image
quality and definition.

On a tripod in low light or hand held in full noon sun.
If hand-held, when highlights are at risk of being blown.

While you can hand hold at that focal length, keep ISO low unless you
don't care about the highlights, then go ahead & boost the ISO (and
overexpose) to take advantage.

Gray duck moving across gray pond with no sky:
-boost ISO and overexpose (then dial down in post).

Alpine sunset at dusk with beautiful bright sky and clouds:
(and almost all scenes with a sky or important highlights)
-keep ISO low and use a tripod when needed.

No argument with anything you've said of course, Paul. The OP said he knew
"relatively little" about the technical aspects and I took his question to
mean he wanted a fairly simple answer about ISO settings.

I'm reminded of a fellow I sold a Mamiya Sekor to 40+ years ago. He clearly
knew very little about cameras but had heard that a "35mm SLR" was the best
kind and wanted one for that reason. When I questioned whether he was ready
for such a camera he assured me that he would quickly "learn all about it"
since he was taking a course in photography at the local community college.

When I saw him some time after that he showed me some photos and I wondered
why he was getting such limited DOF in what was obviously bright sunlight --
he had the standard 55mm f/1.8 lens only. Then he mentioned he used 1/1000
second (top shutter speed on that camera) ALL THE TIME. He was amazed when I
told him I rarely if ever used 1/1000 myself. He apparently figured, that
nice fast shutter speed was there so why use anything less? I don't think he
learned much in the way of fundamentals at that photography course.

Remembering that, I didn't want the OP here to dial in higher than necessary
ISOs just "because they're there." His question suggested he did not know
what drawbacks there might be.

"John Sheehy" wrote in message
...
Paul Furman wrote in -
september.org:

Alpine sunset at dusk with beautiful bright sky and clouds:
(and almost all scenes with a sky or important highlights)
-keep ISO low and use a tripod when needed.

As computers/storage/firmware get faster, we could be shooting 16 ISO 1600
shots in rapid succession for an aligned ISO 100 composite, for a less
read
noise, and less camera shake blur, than "normal" ISO 100.

That's no bargain. That exposure is 4x as long as a single ISO 100 shot, not
counting 15 additional starts and stops. (The world is divided into 10 kinds
of people: those who get it, and those who don't.)

John Sheehy wrote:
(Ray Fischer) wrote in
John Sheehy wrote:

It's the lower exposure, due to the
metering for the higher ISO in auto-exposure modes, which increases
noise, relative to signal.

Inane quibbling.

It's not inane, because the common layperson's model leads to false
conclusions.

False conclusions like "higher ISO makes for noiser pictures"?

In most CMOS DSLRs, higher ISOs are cleaner, in terms of what
noise the *camera* introduces into the exposure.

You are an idiot. Would you like to know why you're an idiot?

--
Ray Fischer

(Ray Fischer) wrote in news:4b985b3a$0$1584
:

You are an idiot. Would you like to know why you're an idiot?

Because you think I'm an idiot, because that's the only way your ego can
deal with correction.

"John Sheehy" wrote in message
...
"Neil Harrington" wrote in
:

Image noise increases at high ISO. At some point this may make the
picture unacceptably grainy, depending on what you consider
acceptable. Most people prefer to use the lowest ISO practicable, for
best image quality and definition. There may be "artistic" reasons to
do otherwise, of course.

Perhaps, but you can add much better-looking noise in software than the
ugly read noise artifacts - unless, of course, you *want* ugly readout
artifacts, in which case, you will do better by under-exposing base ISO on
many DSLRs.


Definitely, ISO 3200 would produce more noise than ISO 400.

It's more like an actual exposure index of 3200 results in 1/8 the
exposure, with a higher resulting SNR. The electronics at ISO 3200 do not
add any more noise than 400 in DSLRs, relative to signal. This may sound
pedantic, but your choice of the word "produce" actually creates an
incorrect statement. The camera doesn't produce more noise at higher ISOs
(except for some P&S cameras); the lower absolute exposure (lesser photon
collection) produces the lower SNR.

Not disputing what you say at all, John, but I think discussion at this
level far exceeds the scope of the OP's question. He wrote:

"I know relatively little about the technical workings of digital
photography, and
[ . . . ] I would like to understand what happens in my camera when I change
the ISO setting.

"I am hoping that once I understand that, I will know the (potential)
disadvantages of always shooting at high ISO, if there are any."

As a practical matter, ISO 3200 does produce more noise in the final result
than ISO 400. I don't think the OP at this point in his photography is
particularly interested in the arcane details of why and how this happens,
whether the noise increase is caused by the electronics or not, how the
signal/noise ratio or volume of photon collection are involved, etc. Of
course I could be mistaken, but my impression is that he just wanted a
fairly simple answer to a fairly simple question.

"MikeWhy" wrote in
:

"John Sheehy" wrote in message
...
Paul Furman wrote in
- september.org:

Alpine sunset at dusk with beautiful bright sky and clouds:
(and almost all scenes with a sky or important highlights)
-keep ISO low and use a tripod when needed.

As computers/storage/firmware get faster, we could be shooting 16 ISO
1600 shots in rapid succession for an aligned ISO 100 composite, for
a less read
noise, and less camera shake blur, than "normal" ISO 100.

That's no bargain. That exposure is 4x as long as a single ISO 100
shot,

No; total exposure time is exactly the same. ISO is linear.

not counting 15 additional starts and stops.

Well, this was a context where everything got faster ...
I believe that there is a new P& or 4/3 camera that does something like
this now. If it is truly a "tripod" type shot, then the extra time is not
much of an issue. You'll just have hyphenation of anything moving against
the background, though.

(The world is
divided into 10 kinds of people: those who get it, and those who
don't.)

Just a bit ...

John Sheehy wrote:
(Ray Fischer) wrote in news:4b985b3a$0$1584
:

You are an idiot. Would you like to know why you're an idiot?

Because you think I'm an idiot, because that's the only way your ego can
deal with correction.

Wrong on both counts.

You're an idiot because you think that it matters where the noise
comes from. It doesn't. It matters how much noise is in the
resulting image. Increasing ISO increases noise in the image.
Idiotic nonsense about how the camera does introduce the noise is
of not the slightest relevance.

--
Ray Fischer

John Sheehy wrote:
(Ray Fischer) wrote in news:4b985b3a$0$1584
:

You are an idiot. Would you like to know why you're an idiot?

Because you think I'm an idiot, because that's the only way your ego can
deal with correction.



In this case, one might see more than a tad of projection by Ray.

--
john mcwilliams

John McWilliams wrote:
John Sheehy wrote:
(Ray Fischer) wrote in news:4b985b3a$0$1584
:

You are an idiot. Would you like to know why you're an idiot?

Because you think I'm an idiot, because that's the only way your ego can
deal with correction.

In this case,

Go away, asshole troll.

--
Ray Fischer