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Hi,guys
Is there some difference about measuring ISO among different company
dc or model? or they all have almost the same sensitivity given the
same ISO number? In my memory, there are some different method related
canon products, but can't find it in their webpage now.

---
regards

Well...there isn't supposed to be. ISO is an acronym for a standards setting
organization. If there are variations they aren't doing their job. But, some
camera are off a bit because manufacturers think that snapshooters will get
a higher number of acceptable photos if they under or over expose....I
forget which. (all from old memories...not neccessarily factual)

--
Thanks,
Gene Palmiter
(visit my photo gallery at http://palmiter.dotphoto.com)
freebridge design group

"maTheMatic" <> wrote in message
news: ps.com...
> Hi,guys
> Is there some difference about measuring ISO among different company
> dc or model? or they all have almost the same sensitivity given the
> same ISO number? In my memory, there are some different method related
> canon products, but can't find it in their webpage now.
>
> ---
> regards
>

"Gene Palmiter" <> wrote in message
news:Q20rg.4474$0V1.3282@trndny06...
> Well...there isn't supposed to be. ISO is an acronym for a standards
> setting organization. If there are variations they aren't doing their job.
> But, some camera are off a bit because manufacturers think that
> snapshooters will get a higher number of acceptable photos if they under
> or over expose....I forget which. (all from old memories...not
> neccessarily factual)

Agreed.

Another problem is that it's almost impossible to compare, since all
metering systems other than spot metering (used by someone who knows what
they are doing) are essentially random guessing games.

Dpreview claims that Canon is consistently more sensitive than the claimed
ISO levels, but I really doubt it. There are ISO standard procedures for
measuring ISO in digital cameras, and I really doubt that Phil is using
them.

David J. Littleboy
Tokyo, Japan

> Is there some difference about measuring ISO among different company
> dc or model? or they all have almost the same sensitivity given the
> same ISO number? In my memory, there are some different method related
> canon products, but can't find it in their webpage now.

I think I know the web page that you are referring to. If it's the same
one that I'm thinking of, the guy took an expensive, calibrated meter, took
shots at different exposures, and calculated the actual ISO that the camera
was using, and the Canon model was, in fact, using a higher ISO than the
simple "100/200/400/etc/".

Ah, this is it:

http://www.imaging-resource.com/PRODS/E5D/E5DA13.HTM

Scroll down to "ISO accuracy".

The short version is that yes, the Canon 5D (and probably other models)
are shooting at a higher ISO than indicated. Instead of
50/100/200/400/800/1600/3200, it's closer to 64/125/250/500/1000/2000/4000/

steve

maTheMatic wrote:

> Hi,guys
> Is there some difference about measuring ISO among different company
> dc or model? or they all have almost the same sensitivity given the
> same ISO number? In my memory, there are some different method related
> canon products, but can't find it in their webpage now.
>
> ---
> regards
>

The light meter's response in a camera is defined by ISO standards,
International Standard ISO 2720: Photography - General
purpose photographic exposure meters (photoelectric
type) - Guide to product specification. First edition 1974.

The basic equation is::
lux = 12.4 * pi * f/#2 / (R * t * exposure_time * ISO),
where f/# is the f/number of the camera lens, exposure
time is in seconds, ISO is the ISO speed, R = reflectance
of the target, t = lens transmission, and pi = 3.14159.

The problem is that the "constant, 12.4 in the above equation,
is not a constant. Different manufacturers can use different
numbers. I've seen references to numbers as high as about 15,
and a little lower than 12. So there is almost a
50% "slop factor" built into the definition.

Reference:
Digital Cameras: Counting Photons, Photometry, and Quantum Efficiency
http://www.clarkvision.com/imagedeta...photons.and.qe

Roger