ISO setting on a dslr?

Why is there an ISO setting for a dslr? I always set my ISO setting for tha
appropriate film I used, but without film, why bother with ISO?

Thanks in advance.

On Tue, 27 Dec 2005 14:19:30 -0500, "shipping"
wrote:

Why is there an ISO setting for a dslr? I always set my ISO setting for tha
appropriate film I used, but without film, why bother with ISO?

Thanks in advance.



Increasing the ISO will permit you to use a faster shutter speed with
the same aperture or to use a smaller aperture with the same shutter
speed. This is useful in situations where flash is not permitted, for
example, churches or museums.

Increasing the ISO may increase the noise in the photograph.

Jack

In article Xsgsf.8527$mK.5522@dukeread03, shipping
writes
Why is there an ISO setting for a dslr? I always set my ISO setting for tha
appropriate film I used, but without film, why bother with ISO?

It defines the sensitivity. More importantly: so that you can have the
shutter (motion freezing or blurring) and depth of field you require
(differential focus) without blowing highlights or loosing too much in
the shadows; unlike film where you have to decide before you load-up and
go out, with dSLR you can vary it from frame-to-frame. I do wish my dSLR
would let me select and adjust ISO setting in the same way I change
shutter and aperture.

--
Ian G8ILZ

Thank you Jack. Is there a standard ISO setting for a dslr?


"Jack Dale" wrote in message
...
On Tue, 27 Dec 2005 14:19:30 -0500, "shipping"
wrote:

Why is there an ISO setting for a dslr? I always set my ISO setting for
tha
appropriate film I used, but without film, why bother with ISO?

Thanks in advance.



Increasing the ISO will permit you to use a faster shutter speed with
the same aperture or to use a smaller aperture with the same shutter
speed. This is useful in situations where flash is not permitted, for
example, churches or museums.

Increasing the ISO may increase the noise in the photograph.

Jack

On Tue, 27 Dec 2005 14:55:31 -0500, "shipping"
wrote:

Thank you Jack. Is there a standard ISO setting for a dslr?


Not really. I keep my ISO as low as possible.

Jack

"shipping" wrote in message
news%gsf.8537$mK.5669@dukeread03...
Thank you Jack. Is there a standard ISO setting for a dslr?

In theory, 100 gives less noise than 200, but in practice it's very hard to
tell the difference. On Canon 350D, 20D etc 400 is also VERY good - 800
starts to show a bit of "grain" (but it really depends on how big the photo
is printed/displayed) - and 1600 / 3200 (20D) in my opinion look pretty
rough, but you can have a good degree of success cleaning up in photoshop
using noise filters.

In message ,
"C J Southern" wrote:

"shipping" wrote in message
news%gsf.8537$mK.5669@dukeread03...
Thank you Jack. Is there a standard ISO setting for a dslr?

In theory, 100 gives less noise than 200, but in practice it's very hard to
tell the difference. On Canon 350D, 20D etc 400 is also VERY good - 800
starts to show a bit of "grain" (but it really depends on how big the photo
is printed/displayed) - and 1600 / 3200 (20D) in my opinion look pretty
rough, but you can have a good degree of success cleaning up in photoshop
using noise filters.

It's not just the ISO per se that determines noise; it also depends
highly on the relative exposure level at that ISO. An ISO 1600 shot of
a white object with grey lettering on it, exposed well, will have less
noise than an ISO 200 shot of the same scene that is average-metered on
a DSLR with relatively clean amplification.

Looking at it another way, the absolute exposure determines the original
signal-to-noise ratio in the sensor, and the higher the ISO, the more
numbers are used to represent luminance in any given shadow range, and
the cleaner those shadows will be. Low ISOs are never a good
alternative when they result in under-exposure.

Some people have accused me of looking at things backwards, but really,
this is how things are really happening in the camera. An
ISO-independent exposure is taken in the sensor, based soley on subject
lighting, f-stop, and shutter speed. At this point, ISO only has one,
single and indirect effect - it affects metering. ISO does not play a
role again until the data is read out and digitized; at ISO 1600, about
1/16th the range of sensor voltages becomes the RAW numbers up to 4095
(through higher amplification); at ISO 100, roughly all of them. So, if
your sensor exposure only uses half the range, shooting at ISO 100 would
be image-destructive, as compared to shooting at ISO 100. If only
1/16th the range is used, ISO 1600 will give the highest quality
results. Once you understand this, you can make more optimal
exposure/ISO decisions.
--


John P Sheehy

"shipping" wrote in message
news:Xsgsf.8527$mK.5522@dukeread03...
Why is there an ISO setting for a dslr? I always set my ISO setting for
tha
appropriate film I used, but without film, why bother with ISO?

For the same reason that you chose the ISO of your film.

As anyone using an film camera ought to know, higher ISO numbers mean
greater sensitivity to light, but also usually mean some loss of sharpness.
So you choose a particular ISO of film to best suit the lighting conditions
under which you'll be shooting.
The ISO setting on a film camera is simply to tell the camera the ISO
rating of the film you're using, which allows the camera to adjust automatic
settings to the film. And quite a few SLRs don't actually have an ISO
setting; they automatically read the film cartridge, and adjust themselves.

The ISO setting on a DSLR doesn't serve the same purpose; instead, it's
the digital equivalent of choosing the ISO of your film.
Same as with film, setting a higher ISO gives higher sensitivity to light,
but you'll lose some sharpness.
IOW, in circumstances where I would load my film camera with 200-speed
film, I'll set the DSLR's ISO to 200. If I find that doesn't give me a fast
enough shutter speed (I'm usually shooting high-speed dog sports, and flash
is prohibited), I'll up the ISO, knowing my pictures will be a bit grainer
but I won't get motion blur.

The beauty of the DSLR, in that respect, is that you can change ISO from
frame to frame as shooting conditions warrant, whereas with a film camera
you have to change the entire roll of film.

In message ,
wrote:

So, if
your sensor exposure only uses half the range, shooting at ISO 100 would
be image-destructive, as compared to shooting at ISO 100.

Whoops! That last 100 should have been 200.
--


John P Sheehy

I (think I) understand what you're saying, but ...

.... let's see if I've got this right ...

"If I take 6 shots - one at each available ISO on my 20D - and each are
correctly exposed so that the full tonal range is used - then the lower ISO
will always have the lower noise".

However ...

"If I'm struggling to get a shot in poor light - in terms of noise - I'm
always better off to use a a higher ISO than to have an image more than a
stop under exposed at 1/2 that ISO"?

Cheers,

Colin