Re: Spectrophotometer accuracy
Re: Spectrophotometer accuracy
- Subject: Re: Spectrophotometer accuracy
- From: <email@hidden>
- Date: Thu, 25 Aug 2005 22:32:28 -0400
Michael,
Using an Eye-One, there is a simple test to prove that
there is an internal safegard for calibration. Simply
"un-seat" the spectro on its tile base(just a little); you
will generally have a message that calibration failed.
Having programmed for such devices, I can tell you that
this message comes from the device/driver, not the
application which has no control on the returned
calibration data.
I also saw an Eye-One which did not pass reflectance
calibration, when perfectly seated, even though its
light-source was working (BTW, this unit worked OK in
emission mode). This Eye-One required a factory
repair/re-cal.
As you mention, there is likely reference values stored in
the device itself. Someone from GMB could confirm that,
but it only makes manufacturing and physical sense. Also,
a similar set of references is likely used for the ambient
attachment.
Does this assure that your instrument is within spec?
25% over spec? 50% over spec?
It certainly helps but it is hard to confirm without
information from the manufacturer, which must consider it
competition sensitive!
However, as I calculated in my first response, your
results are in the ball park.
Danny Pascale
email@hidden
www.BabelColor.com
P.S. I also noticed that calibration could be affected by
a strong side-light, such as a desk lamp or a bright LCD
monitor, illuminating the spectro on its base. To prevent
any problems I usually close as many lamps that I can when
I calibrate (minimizing ambient light is also a valid
procedure during a measurement of course!).
On Thu, 25 Aug 2005 16:33:37 -0700
"Michael Fox Photography News Account"
<email@hidden> wrote:
WoW! Thanks for everyone's input. Let me ask a more
fundamental question.
When using each instrument, both MeasureTool and i1
Share have a
"calibration" step where the instrument is placed on
it's own respective,
serial-numbered, white tile.
Can someone describe what is happening at that step? I
mean, is the reading
of the white tile being compared to some value stored in
non-volatile memory
of the device?
If that step passes (which it does), can I be assured
that the instrument is
now proven to be operating within it's tolerance band?
If so, then I know the true value must be somewhere in
the intersection of
the tolerance bands of the two instruments.
However, if the "calibration" step does not prove beyond
a doubt that the
instrument is operating within its tolerance band, then
I don't know what
the "calibration" step is telling me.
Michael
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