Re: Spectrocam and UV
Re: Spectrocam and UV
- Subject: Re: Spectrocam and UV
- From: Roberto Michelena <email@hidden>
- Date: Mon, 11 Jun 2001 17:30:24 -0500
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Please clarify some heresay and ideas in my head.
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I've heard that the Spectrostar Spectrocam has a UV filter on the light
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coming OUT of the device.
Morgan, as far as I know this is not true; all the contrary, due to the
Spectrocam's D65 light source, it emits MORE UV light than other
spectrophotometers.
For the Gretag SpectroLino (whose automation table is called SpectroScan)
you can indeed buy such a filter as an option. And it's removable.
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If this is the case, wouldn't papers that floresce still bounce back light
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outside the visible spectrum and cause the problems that UV filter is there
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to prevent?
The "fluorescence problem" is not that the papers bounce light outside of
visible spectrum, but all the contrary: that light emitted outside the
visible spectrum (as UV light) be bounced back as visible (usually blue).
So when you use a UV filter, it is always on the light coming out of the
device (so that it doesn't reach the paper), not on the reflection coming
in.
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I have a customer looking to purchase a profiling package and I am hesitant
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in suggesting the Spectrocam if there would be problems with the super
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bright papers in his RGB photo process printer.
Now comes the hard part: to filter or not to filter. There have been
heated discussions before on the subject. Natural daylight has more UV
than D50, and certainly more than UV-filtered D50. So by placing such a
filter, you are making your spectro's light source even more different
from daylight than it already was.
The Spectrocam, on the other hand, has a pulsed Xenon lamp with a
spectral curve that closely matches D65, and that has more UV than D50.
Might be much more similar to daylight than other spectro's light source.
So it seems the Spectrocam would make the papers fluoresce even more.
And it seems that would be better since it's more alike the conditions
under which your customers will be looking at the prints.
And indeed, according to users, some of them very experienced, that gives
them a better result. No problem with optical whiteners.
Probably the thing has to do with D65 to D50 conversion math? I don't
have a Spectrocam, so I haven't been able to experience the difference
myself.
But on the other hand, non-Spectrocam devices, all of them behave badly
in the presence of fluorescence. They read your paper as blue, and not as
bright as it should.
I've tried UV filters, Polarizer filters and D65 filters on the
SpectroLino. They do make difference, and for optical brightener
certainly the UV filter does help, since the white point will be read
less blue (more neutral).
Hope this hasn't made waters more muddy. It's still an open issue for the
whole colorsync community, I believe.
best regards,
-- Roberto Michelena
EOS S.A.
Lima, Peru