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Re: Green Light



In a message dated 98-03-13 10:53:44 EST, Peter Swinson wrote:

<< The output of a CRT is not green light, it is broadband light, albeit with
a green bias, just as the Xenon is broadband light with a blue bias.  It is
not the same as putting a filter on the camera lens, which will only allow
through light of that colour. >>


Hi Peter,

In all types of telecines, filtering is exactly what does happen.  Since no
known type of CCDs, PMTs, or other light sensors respond to light of only one
color, any practical telecine must contain beam splitters and filters ahead of
the sensors.  Different film bases act as additional filters, as is evidenced
by transferring negative, internegative, or interpositive stocks.  Unless the
splitter and filters are optimized for the film being transferred as well as
the light source, there isn't much point in worrying about anything else.
Consequently, it appears that telecines which only have one set of filters and
a light source of only one color spectrum are more limited in the range of
film stocks and images they can handle before the signal-to-noise ratio goes
into the dumps.

Best regards,
Christopher Bacon

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