How to measure ISO

In article , Floyd L. Davidson says...
if iso 100 on one camera is not the same as iso 100 on another camera
or the same as with film, then the number is meaningless.

Okay, it works well for everyone except you.

As explained, one of the cameras produces a brighter image at the same
ISO, aperture and exposure time settings.

Not a big problem, but the question is which camera has the correct ISO
setting, of if perhaps both cameras deviate from the true ISO 100.
--
Alfred Molon

Olympus E-series DSLRs and micro 4/3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site

On Tue, 27 Oct 2015 20:07:15 +0100, Alfred Molon
wrote:

I have two cameras. At the same ISO, aperture and exposure time one
takes brighter images than the other one.

How to measure the real ISO values at which the cameras took the
pictures?


Shoot a grey scale using sunny sixteen values, maybe.

On Tue, 27 Oct 2015 20:07:15 +0100, Alfred Molon
wrote:

I have two cameras. At the same ISO, aperture and exposure time one
takes brighter images than the other one.

How to measure the real ISO values at which the cameras took the
pictures?


Borrow or rent an external light meter, compare the values. Then you
can have three variables.

On 29/10/2015 22:27, Alfred Molon wrote:
In article , Floyd L. Davidson says...
if iso 100 on one camera is not the same as iso 100 on another camera
or the same as with film, then the number is meaningless.

Okay, it works well for everyone except you.

As explained, one of the cameras produces a brighter image at the same
ISO, aperture and exposure time settings.

Not a big problem, but the question is which camera has the correct ISO
setting, of if perhaps both cameras deviate from the true ISO 100.

Well you could take a reputable exposure meter and see which camera
agrees with it better.

On 10/29/2015 6:52 PM, newshound wrote:
On 29/10/2015 22:27, Alfred Molon wrote:
In article , Floyd L. Davidson says...
if iso 100 on one camera is not the same as iso 100 on another camera
or the same as with film, then the number is meaningless.

Okay, it works well for everyone except you.

As explained, one of the cameras produces a brighter image at the same
ISO, aperture and exposure time settings.

Not a big problem, but the question is which camera has the correct ISO
setting, of if perhaps both cameras deviate from the true ISO 100.

Well you could take a reputable exposure meter and see which camera
agrees with it better.

Maybe.
Certainly a center weighter system would give a different reading than a
matrix, or average system. Even with center weighted systems the overall
exposure would differ with the size of the center.

--
PeterN

On Thu, 29 Oct 2015 20:43:41 -0400, Tony Cooper
wrote:

On Thu, 29 Oct 2015 23:27:18 +0100, Alfred Molon
wrote:

In article , Floyd L. Davidson says...
if iso 100 on one camera is not the same as iso 100 on another camera
or the same as with film, then the number is meaningless.

Okay, it works well for everyone except you.

As explained, one of the cameras produces a brighter image at the same
ISO, aperture and exposure time settings.

Not a big problem, but the question is which camera has the correct ISO
setting, of if perhaps both cameras deviate from the true ISO 100.

While you may have a point, it would not affect me to know that the
ISO setting in my camera is 100 off or not. I know what I can expect
from a setting, and set the camera accordingly.

Things worked just as well in the days I set my exposure to the Weston
scale. The numbers don't really matter but when you have more than one
camera its nice if they share a common scale.
--

Regards,

Eric Stevens

In article , Floyd L. Davidson
wrote:

No cameras "cheat". The Standard basically says that any method
the manufacturer likes, is okay. That makes cheating not only
unnecessary, but virtually impossible.

then there is no standard.

And in fact it's a system that has turned out to work well
enough over the years!

clearly not.

if iso 100 on one camera is not the same as iso 100 on another camera
or the same as with film, then the number is meaningless.

Okay, it works well for everyone except you.

take two cameras and set them to the same exposure. if one photo is
brighter than the other, then the iso of at least one of the cameras is
wrong.

it's a competitive advantage to claim better performance at high iso
than other cameras, and some camera makers do exactly that, fuji being
one of them.

http://farm9.staticflickr.com/8358/8363870696_ef5f38094a_b.jpg

In article , Tony Cooper
wrote:

if iso 100 on one camera is not the same as iso 100 on another camera
or the same as with film, then the number is meaningless.

Okay, it works well for everyone except you.

As explained, one of the cameras produces a brighter image at the same
ISO, aperture and exposure time settings.

Not a big problem, but the question is which camera has the correct ISO
setting, of if perhaps both cameras deviate from the true ISO 100.

While you may have a point, it would not affect me to know that the
ISO setting in my camera is 100 off or not. I know what I can expect
from a setting, and set the camera accordingly.

for one camera, perhaps, but that number may not be the same on other
cameras. for those who use light meters and/or studio lighting, they
may also need to adjust the readings.

In article , Eric Stevens
wrote:

Not a big problem, but the question is which camera has the correct ISO
setting, of if perhaps both cameras deviate from the true ISO 100.

While you may have a point, it would not affect me to know that the
ISO setting in my camera is 100 off or not. I know what I can expect
from a setting, and set the camera accordingly.

Things worked just as well in the days I set my exposure to the Weston
scale. The numbers don't really matter but when you have more than one
camera its nice if they share a common scale.

exactly the point.

On 2015-10-28 15:48, Alfred Molon wrote:
In article ,
newshound says...
Or are you saying that you have a camera without such an adjustment, and
you are trying to demonstrate that it is faulty?

I meant that these two cameras, if set at the same ISO value, aperture
and exposure time should deliver an image with the same brightness
value.
But one of the cameras creates a brighter image, even in RAW (if
applying the same RAW conversion parameters).

In other words either the ISO 100 of one camera is in reality an ISO 80
or an ISO 125 and the other camera is accurate, or both cameras deviate
a bit from the ISO.


Back when I bothered to read dpreview there was lots of mention on the
disparity of ISO sensitivity between camera makers or even cameras from
the same co.

Whether this is due to their interpretation of the method, sensor design
or optimization to make particular models stand out at a given ISO
number is anyone's guess.

And it is not at all important.

You can do a standard candle test, if you like. Shoot a grey card in
direct sunlight. Should give you a sunny-16 exposure. Deviance from
that represents "error". That said, the variance in grey cards that I
have spans a full stop or more...

What is important is testing your camera in various lighting situations,
understanding its metering system and if you're a noise-peeper figuring
out what ISO is the quietest. (On my preferred camera that would be ISO
160).