Re: ProfileMaker 5
Re: ProfileMaker 5
- Subject: Re: ProfileMaker 5
- From: Robin Myers <email@hidden>
- Date: Tue, 15 Aug 2006 10:15:26 -0700
Dear Mr. Breton,
I use the D65 filter for several reasons.
First, the illumination in the Spectrolino is a standard
tungsten-halogen bulb, thus very deficient in the blue and violet
spectral region. The D65 filter changes the ratio of blue light in the
illuminant, ostensibly to achieve a D65 simulated illuminant. My
sources at Gretag have stated that it does not really achieve a full
D65 simulation, but it gets close to a D50 simulated illuminant. I have
not had the time to confirm this with my own measurements but it does
sound plausible.
Second, many of the experiments I have made with regard to UV
excitation and fluorescing subjects show that using the D65 filter
causes much more excitation than the U filter. Try this for yourself
with a FWA brightened paper measured with the D65 and U filters. Using
the D65 filter produces a much more pronounced fluorescence.
Third, using the U filter would require the signals at the violet and
blue ends of the spectrum to be heavily amplified, increasing the noise
in these signals. The Spectrolino automatically increases the
integration time when the D65 filter is present to improve the signal
to noise ratio, thus compensating for the reduced light transmission,
resulting in a more even distribution of noise across the spectrum.
By the way, the U filter is not merely an empty tube, it contains a
piece of clear glass. So optically it is effecting the instrument in a
similar way to the other filters with regards to refraction and focus.
A small effect to be sure, but it shows the attention to detail of the
Gretag engineers in their pursuit of good measurements.
Regards,
Robin Myers
On Aug 15, 2006, at 9:36, Roger Breton wrote:
Measured with a Spectrolino equipped with the D65 filter, average of
4 measurements each, white backing; calculated by SpectraShop 2 with
2 degree observer, D50 illuminant.
Robin Myers
Dear Robin,
Pardon me for asking what may seems like an obvious question to you and
others on this list but what's the benefit of measuring with the D65
filter
on your Spectrolino? As opposed to measuring with only the U attachment
mounted onto the head of the instrument (the U is just a hole that
covers
the some of the head opening on the 'Lino, resuting in no filtration
whatsoever, just the pure tungsten lighting)? Are you're trying to
excite
more fluorescence out of the substrate that way? Would you have gotten
filgures with smaller b* values otherwise?
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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