Hutech Astronomical Products
Equipment for the Serious Amateur Astronomer



Astro Camera FAQ

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).

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