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Re; Green Light



Dear All,

The comments made regarding the suitability of the Xenon lamp as
the light source for film scanning seem to be at odds with our current 
experiences.

The use of such a variable intensity device in the Spirit produces far 
superior signal to noise results across all three channels than the
current CRTs in the Golds.  No doubt the PEC replacements in the
forthcoming CReality will offer a level of conversion of its CRT output
that will be also be an improvement on the Gold but the fundamental
advantages of the blue rich source, as detailed by Mikael Reichel in 
his elegant posting, will still be missing.  

Also, as Spirit users already know, the design of the machine requires
that the lamp is only on when the film is in motion and thus any single
frame is within the  "concentrated slit of light "  for a 24th or 25th of a

second. As you run at much lower speeds for Data transfers, about
4 to 5fps, the lamp intensity is reduced. ("Exposure" is a function of lamp
intensity and servo speed. It can be useful to recheck illumination levels
prior to a data transfer because of this.) Scenes from OCN that we have
used repeatedly in our Data path show no sign of any layer damage at
all, indeed the only remarkable thing about them is that they match exactly
to original Data and D1 transfers from last  March depite firmware and
software changes and, more importantly, a Xenon lamp change.
To suggest that only a CRT, which illuminates a still frame at all times,
is the only  "protecting",  ie safe, illumination source is very
misleading.

Experience has also shown that the xenon lamp allows for a far greater 
range of colour reproduction especially of the blue / green half tones
which even the fixed masking of the Golds cannot reproduce. The practice
of using the Ursa six vector SCC as a further set of masking coefficients
is thus avoided along with the ensuing increase in noise. It is quite
possible to match images from a six vector corrected Ursa D1 using the
Spirits illumination and neg matching controls in order to produce a 
Data transfer for the cinema version of a commercial.

The imaging head of the Spirit is really the responsibility of Kodak whose
design criterior was to match the RGB curves from the telecine to 
those of the film and thus increase the reponse from the blue and red
channels. The xenon lamp seems to be more than capable of this.

Regards
Seamus O'Kane
VTR Ltd. London.

The above viewpoints are my own, and are unbeholding to all. 

---
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953 subscribers in 36 countries on Sun Mar 15 16:01:12 PST 1998
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