Switching to D - How does ISO work?

I have been using my trusty Nikon F2AS and about 15 or so lenses for
it since about 1980. Being a big fan of Photoshop and seeing the
quality of a number of digital cameras, I have decided to take the
plunge and retire the trusty F2AS in leiu of a Nikon D100. Now, I
know almost nothing about Digital photography other then the
information that I have read on the net and the beautiful images I
have seen this camera create.

My question is this: Is the CCD rated at some specific ISO/ASA? Is
that setting adjustable if it is? The D100 has shutter speeds and
obviously my lenses have a speed or maximum aperature rating as well
as having an aperature (with 2 exceptions of catadioptric lenses).
Therefore exposures must be calculated based on the sensitivty or
speed of the CCD.

Any infor or links to sites that might discuss this would be GREATLY
appreciated!

TIA!

Mike

 

Have you looked at http://www.dpreview.com/reviews/nikond100/

. Auto (200 - 1600) - enabled via custom func.
. ISO 200
. ISO 250
. ISO 320
. ISO 400
. ISO 500
. ISO 640
. ISO 800
. ISO 1000
. ISO 1250
. ISO 1600
. HI-1 (~ISO 3200)
. HI-2 (~ISO 6400)

ISO in a digital camera is set by the gain of the amplifier before the
analog to digital converter. High gain translates to high sensitivity and
high ISO. Hope this helps.

 

The ISO is adjustable, but the adjustment is made by cranking up the signal
amplifier, and the more amplification, the more noise. Treat it like your
choice of film ISO and select the lowest one that lets you achieve the
settings you want. The big benefit is that you can change it between each
shot, instead of having to use up a whole roll before switching to a different
speed.

I think you'll find up to ISO 400 looks excellent, beyond that it starts to
get noisy, but so does 800+ speed film.

Ken

 

ISO in digicams is simply the amount of amplfier gain applied to the signal
coming from the sensor. In general, increasing the gain also increases the
noise -- also known as digital grain. Most digicams are terrible at higher
ISOs. The normal base ISO seems to be 100 but some start at 50.

Look here for a review of the D100's ISO performance compared to a Canon
D60:
http://www.dpreview.com/reviews/nikond100/page16.asp

Good Luck!

 

Yes. ISO 200 (100 not available on the D100.)

Yes, from 200 all the way up to 6400 (which
Nikon oddly calls "High 2", "High 1" being 3200.)

....up to 1/4000.

 

Are you sure of that? Have you tryed testing by changing ONLY the
ISO and comparing the output data?

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

 

Ken is correct. DPReview has done the testing for you.
http://www.dpreview.com/reviews/nikond100/page16.asp

 

Mike,

| My question is this: Is the CCD rated at some specific ISO/ASA? Is
| that setting adjustable if it is? The D100 has shutter speeds and
| obviously my lenses have a speed or maximum aperature rating as well
| as having an aperature (with 2 exceptions of catadioptric lenses).
| Therefore exposures must be calculated based on the sensitivty or
| speed of the CCD.
|
| Any infor or links to sites that might discuss this would be GREATLY
| appreciated!

Ken Alverson put it succinctly, but I'll try to elaborate a bit.

Yes, each CCD has certain base sensitivity measured in something like
voltage per unit light input. (If Dave Martindale were around, he
could supply accurate details.) Some are slightly more sensitive than
others, depending on design features like sensel area and depth and
substrate thickness, but the base photosensitivity of silicon brackets
the variation. The tiny analog CCD output voltages must be amplified
up to levels suitable for digitization, storage and display. Digital
camera engineers work hard to match their amplification levels with
ISO numbers so that their camera speeds match the expectations of
photographers used to ISO speed calibrations long established on the
film side. Thus, you can take a digital camera's current ISO setting
as the effective speed of its CCD plus associated electronics. You may
then work with aperture, shutter speed and your lenses as would with
film of the same sensitivity. Of course, a camera set at ISO 100 may
turn out to act more like ISO 80 under testing, but camera-film
combinations show similar variations.

So far, so good, but as others have pointed out, higher ISO invariably
means higher image noise, and noise only superficially resembles film
grain. Some cameras are less noisy than others at a given ISO, again
due to differences in CCD and circuit designs. (You generally pay big
$$$ for that.) For more details, see

www.cliffshade.com/dpfwiw/exposure.htm#iso

 

In message <>,

I may be wrong, but I've heard that the D100 only goes up to ISO 800,
electrically, and gets the higher ISOs by under-exposing and multiplying
the results. In that case, you may be better off shooting at ISO 800
yourself and underexposing, to preserve more highlights.
--

 

In message <>,

I thought that my Canon 10D had true ISO 1600, but I shot a very dark
frame at ISOs 100 through 3200 and used a program that dumps the raw
data untouched, and the ISO 1600 and 3200 had numbers that were double
the numbers I was getting in 100 through 800. This leads me to conclude
that ISOs 100 through 800 are true (consistent), ISO 1600 is 800 pushed
one stop arithmetically (double the values out of the ADC), and ISO 3200
is 1600 pushed one stop arithmetically.

Now, I'm wondering if enabling "ISO expansion" to get the pseudo-3200
also changes the 1600 from true 1600 to pushed 800. Another experiment
to conduct. If that is true, I will turn off ISO expansion and push it
myself when I want ISO 3200 (or more).
--

 

In message <[email protected]_s51>,

No, they haven't.

You would have to compare not only the output at various ISOs, but with
various pushes and pulls as well, to determine what true (consistent)
ISOs a camera has.
--

 

In message <[email protected]_s54>,

Not exactly. Many cameras just cut the exposure and multiply the
numbers output by the analog-to-digital converter for some of their
higher ISOs.
--

 

Thanks - this is exactly what I was looking for. Did not mean to
start an argument amongst you all tho

 

| Thanks - this is exactly what I was looking for. Did not mean to
| start an argument amongst you all tho

Don't worry, nearly every question here starts an argument. (Different
levels of understanding and misunderstanding often clash.) We're used
to it. Soon you will be, too.

 

nearly every question here starts an argument.

<grin> I prefer to think of them as deeply-felt discussions
by passionate photographers possessed of varying levels
of artistic and verbal skill.

Stan
yep and I loved Hyde Park in London

 

jam, thanks for that informative article. From another relative newbie!

John
On the 'Poco Loco' out of Deale, MD

 

They give SN ratios for changing exposure. I will see if I
can get my hands on a few bodies to run some tests on.

If anyone wants to try, set up a grey patch, and run s set of shots
with MANUAL exposure. Just change the `ISO', do NOT change anything
else then compare the raw data for the shots.

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.