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RE> URSA Color Drift

RE> URSA Color Drift
To "Dave Corbitt" <dc at mte.com>, "telecine group" <telecine at xyzoom.alegria.com>

The color difference when switching stanfards is there on 
all machines I have ever seen.  Sometimes only a keen eye
will see it, but with print where you have some stretch in
the blacks it is apparent.  I battered Rank U.K with this a
long while ago and all they would say was there is a slight
scan line spacing difference between standards and thus a
slight overall light ouput difference that is probably
causing the difference.  Well perhaps the active burn
correction discussion gets a look in here.  We don't don't
tend to re-auto align when switching between standards
We do find that if you auto align once you do not
necessarily get the correct answer.  Our habit these days to
auto align twice.  For some reason this makes a difference
especially after a gate change or power down.
Moving on a little, we at one point had a serious drift
problem on two of our machines.  After putting a chart
recorder in the machine room for a while we found it
followed the temp and humidity predictably.  Spending loads
of dosh on fixing the the air conditioning design improved
things dramatically.
Another drift problem I had was due to a PEC taking it's
time going south.  A couple of my colorists are in the habit
of saving TAF reference corrections daily which help me
track what is going on.
We also put cards in the gate when the machines are idle and
do find that this helps.
I tend never to turn the tubes off as we find it takes more
than an hour for them to totally stabilise.
One last comment.  Those "linear" PEC's, when they drift
sure do give you a non-linear error don'y they.