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RE: Film question

>Has any of you ever tried to lay down side by side one piece of acetate 
>film and one piece of Estar base film? Every time we do, we always 
>end up with a difference of one whole sprocket every 3 or 4 feet

Is it possible you are comparing acetate base negative stock with estar
print base?  There is a difference between these: the perforation pitch on
negative is .1866", whereas it is .1870" on print film.  You would find a
difference of about one perforation height in three feet.

The reason for this is that during printing, negative and raw print stock
pass around a printer sprocket wheel of a certain diameter, and must remain
in perfect contact with no slippage. The print stock is on the outside of
the negative and therefore follows a larger circumference.

There is a minute change in film dimensions during processing and especially
during drying - but this is small compared with the differences we are
discussing here (except in nitrate film!).

  Dominic Case
  Atlab Australia
  email:  cased at atlab.com.au

Thanks to Bill Hogan of Sprocket Digital for support in 1999.
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