Mid Roll Change

Until recently, mid roll change of film is a function seldom available to 35mm camera user. Only very few 35mm camera, such as Zeiss Ikon Contarex, Contaflex has dual film cartridge film back. These special dual cassette film backs allow you to take out one film in the middle and replace it with another.

With other 35mm camera, you can still take the film out in the middle, and reload it later, but you have to mark the last exposed frame number on the film leader, and when you reload it you have to cover the lens with lens cap and fire you camera N number of times to bring it to the proper spot; not convenient at all.

Many high end APS format cameras have MRC function.

MRC with Minox

The dual chamber Minox cassette allows taking out film in the middle and replace it with a different kind of film. For example, if you were taking B&W photos moments ago, now you want to switch to color print film, you can take the film out, mark the last expose number on you photo note book, and put a roll of color film in. Or perhaps your friend wants to borrow your Minox B, but you have unfinished film in it, you can take the film out, lent him the camera and reload the film cassette later. Or your were taking landscape picture with ASA 25 film, now you walk into a museum, you want to change to ASA 400 film, you need MRC.

Many Minox or subminiature photography book did discuss about mid roll change, such as Joseph Cooper's or Rolf Kasemeier's, they said all you have to do is when you reload the MRC film, push-pull 4 times to advance the film.

I have discovered that is not correct. Why ? I shall discuss this point later

-- Anonymous, February 14, 2000

Answers

MRC in 110 aand 126 cartridge film

Minox style dual chamber cassette was later imitated by Kodak 126 and 110 format to some extend. Mid roll change of film for 110 and 126 format is even simpler than APS MRC This might lead people to think than MRC with Minox cassette is the same. But as a matter of fact, it is not so.

MRC with Minox Cassette

MRC with Minox cassette is slightly more complex.

126 and 110 film are perforated, driven by a hook engaging film performation, but the film is not pull by take up spool. On the other hand, Minox 8x11 film is unperforated, and the film is pulled by the take up spool when the camera drive mechanism turns the film drive spindle. Hence the Minox film winds tightly over the take up spool, very much like a wind up main spring in a mechanical clock. The film is under tension. If you try to take out a Minox cassette in the middle, you may find that it is harder than when the film is used to end.

When you take out a Minox film cassette in the middle, the wound up film immediately spring loose like a piece of watch main spring !

When you put that cassette back into the camera, you have to push-pull several times to "wind up" the film, in order for it to wind up tightly on the spool and restore to its original state.

How many push-pull is needed ?It depends on the number of exposure and the thickness of film.

-- Anonymous, February 14, 2000