Converting 120 Film for Astro Camera Use
Astro cameras with vacuum backs must use 220 film
so that the vacuum will properly hold the film flat.
120 film with its paper backing cannot be used.
However, the longer length (2x) and greater expense of the
220 film and processing can be sidestepped by converting
120 rolls as described below. This procedure is also
useful for Tech Pan film which must be hypered without
the paper backing.
What's in a 120 and 220 Film Roll
Both 120 and 220 film are 60 mm wide, mounted on
identical reels, and start with a paper leader which is
cut to fit onto the takeup reel.
With the roll flipped over, the start of the film is
clear. It is taped to the leader paper 17 inches into
the roll. On 120 film rolls, the paper continues along
the full length of the film as a black backing paper.
This paper is not attached to the film except at the
beginning of the roll. On 220 rolls, the leader paper
stops where the film starts. There is no backing paper
in a 220 roll.
At the end of a 220 roll, a paper
end-leader is also taped to the end of the film.
But at the end of a 120 roll, the paper backing itself
goes on to terminate as the end-leader. The end of
the film is not attached to the paper, unlike at the start
of the film.
Converting a 120 Roll
The first step is to attach the leader to a spare reel.
All steps that follow must be done in complete
darkness and without touching the film emulsion or
kinking the film. Use a throw-away roll of film to
practice these steps.
Once in darkness, the film should be rolled onto the
takeup reel until the end of the film is encountered.
At the end of the film, the loose film should be taped
down to the backing paper.
Once the film is taped down, cut the paper behind the
film near the tape as shown below, then roll the film
back onto the original reel without the paper
backing, taking care to insure that the film is
rolled tightly back onto the reel. The backing paper
should accumulate in a roll by itself automatically as
the film is rolled back onto the original feed reel.
When the start of the film is encountered again, cut
the backing paper away (see below) from the film as was
done at the end of the film and finish by rolling the
leader onto the film roll. The backing paper which was
cut off may be discarded.
Last, tape the leader end down to prevent unwinding.
This completes the procedure and the film is ready to
load into the camera, or it may be stored refrigerated
in an airtight container such as a zip lock bag (with as
much air removed as possible).