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Re: spot vs line analyser for telecine



At 11:40 AM 9/7/97 -0000, jpb <aaton.jp at alpes-net.fr> wrote:
>
>Here is something I've been wondering about during the 
>CCD line vs Flying-spot discussions on the TIG.
>
>Would it be true to say that --in theory--,
>the 'dot' illumination of flying spot analysers --which only 
>puts light onto one pixel of the film at a time-- can produce 
>cleaner images than the 'line' illumination used for CCD 
>imagers in which all the clear/transparent areas of the full
>scanned line can be detrimental (through the unavoidable parasitic 
>reflexions in the optical path) to their opaque neighbours purity?

The flying spot writes and having writ moves on. But the photo electric
cell that detects the light variations as the spot moves across the picture
is not scanned and will pickup any light transmitted down the path. This
includes optical flare from the spot's current position that illuminates
surrounding areas of the film. This was the source of a major advance in
the optical path as the thick face plate on the CRT (intorduced on the
URSA) can keep flare from interfering with the spot.

As I understand it, a CCD telecine senses a line from a larger illuminated
patch. The surrounding area could be a contributor to flare but I expect
that both systems have made great efforts to eliminate these problems in
current design.

How about film cameras? Are internal reflections in the lens a significant
problem today?

David Tosh <dlt at earthlink.net>
Engineer, Complete Post Hollywood

+++
	Thanks to Kat Dalton for support of the TIG
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