[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Trouble with.......



Interesting to hear the discussion re drift. Over the many years of working
telecine machines (and fixing them), drift was not a problem (this also applied
also to MK2's!!). Most of the drift in the early days could be attributed to the
faceplate temperature not being stable and did have a marked effect on the
efficiency of the phosphor, which did not track regarding colorimetry or light
output
.
                                        Some of you might be saying in the old
days that was no real problem as transfers where real time only, but this was
not true all of the time as I used a punched tape system (changing the grading
of a scene was done with a razor blade and sticky tape). But this is another
story.
                                        P.M.T's of that time if I remember
correctly where made by EMI and Philips, and did not seem to exhibit drift
tendencies, so what has changed first and foremost seems to be the sensitivity
followed by the noise performance and in my opinion the less said about the
resolution of the pmt's the better. So has the stability of the tubes been
traded of against the other items?.
                                        In our facility we have three MK3'S of
various ages and all of them drift and the environments are different for each
one. We have done some tests on two of them and no solid conclusions reached so
far, note that in the two cases the power input is via an AVR and the room
temperatures kept within two degrees centigrade of nominal, and in both cases
variations up to 3% have been noted in levels usually affecting green and blue
in the blacks on negative. The electronics are stable though.
                                        We do have a "new" colourist who before
joining us worked almost exclusively on documentaries taking up to 12 hours to
grade and he has commented on the lack of stability compared to his  previous
machine on which he could come back a week later and call up a grading and it
would be perfect. But I suppose we are not discussing German made devices, it
would be interesting to hear from someone regarding the FDL series on this
matter.

 All of the above poses yet more questions,

                                       Is it tube?. What are the specs for short
term phosphor stability regarding phosphor temperature remembering also that the
temperature will vary between run and still and the thick faceplate could
possibly exaggerate this,

                                      Or PMT'S does any one know if there is
anything given in the specs regarding short term stability remembering that the
light input is variable and sometimes static for long durations how does it
compare to CCD specs?.

                                    I feel it could be a combination of both
considering that in our case ambient air temperature and voltage fluctuations
can be ruled out, also the machines are left on and in use for up to twenty
hours a day.


Hope this adds some fuel to this issue 

Perhaps other "old timers" could add some more. Any comments say from Mike Orton
(Hi Mike). 

Peter Makosz 
The Machine Room (London)