[rollei_list] Re: [rolleiusers] Argomania
- From: Don Williams <dwilli10@xxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Sat, 16 Jan 2010 18:55:16 -0600
At 04:32 PM 1/16/2010, Ricnard K wrote:
But... There is a difference. while the support is the same the
perforations are different. 35mm motion picture film comes with two
different types of perforations. Negative film is usually perforated
with what are called Bell & Howell perforations. These have flat
tops and bottoms but round sides, essentially circles with the top
and bottom flattened. Positive film like release prints have Kodak
Standard perforations. These are the familiar oblong perfs with
rounded corners. B&H perfs supposedly register more accurately but
the KS perfs take the stress of projection better. For some reason
film for 35mm still cameras always has KS perfs regardless of
whether its negative or positive. Both perfs will run on the same
sprockets so surplus motion picture film can be used in still
cameras with no difference.
A historical note: For a very long time motion picture release
prints were made by contact printing. The printers mostly ran the
two films in contact around the periphery of a large sprocket wheel
with the negative film inside. When the film was processed it
shrunk so the pitch of the perforations was slightly shorter than
it was originally. The diameter of the printing wheel was chosen so
that the slightly larger diameter the raw print stock followed just
made up for the longer perforation pitch. When nitrate film was
replaced by other stock it was found that the newer stock did not
shrink, or at least did not shrink as much as the nitrate, so film
began to be made in two perforation pitches, one for negatives and
another, longer pitch, for positive film. This made the two films
register better on the printer. However, the shorter pitch negative
film tended to be noisy in the camera until cameras were equipped
with adjustable movements to account for the variation.
I think most release printing is done on optical printers now
where the film is not in physical contact.
Makes a lot of sense. Someone with the facts- Thanks for the explanations.
There used to be a company, Seattle Film Works I believe, that made a
business of spooling and processing movie stock ends for still camera
use. I suppose they are gone, but in any case I never got very good
results from them.
DAW
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