There should be a standard to measure the ISO for digital cameras, I believe
it check the grey rendering. For example, the grey card should read 128 (?)
if properly exposed. But they have to first make sure the accuracy of the
grey card and their external meter. Either or both must be wrong if DXO and
DPreview are different. For the maufacturer, they always not follow the rule
for some marketing reasons, like a F2 lens could be F2.1, a 35-80mm lens
just a 36-76mm...
C.H.Ling
----- Original Message -----
From: "Wayne Harridge"
>
>
>> Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
>>
>> That's interesting. DPReview has been reporting actual ISO test results
>>
>> for a long time. DXO says the Canon 5D's ISO 100 is actually 92.
>> DPreview reported it as 125. And, of course, Canons says it's 100.
>> Who's right? I doesn't make any difference until I have to get out the
>> external meter for flash.
>>
>
> A couple of points:
>
> What was the actual film speed of Kodak Portra 400 ?
> Would anyone really notice if it was 380 or 420 ?
> How much variation is there from batch to batch ?
> Is there an actual ISO standard for measuring the "speed" of a digital
> camera ? There is for film, but since the "characteristic curve" (from
> which the film speed is measured) is different for film and digital I
> doubt you can just directly apply the film standard to a digital sensor.
>
> ...Wayne
>
> Wayne Harridge
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