Where I am, It is hard to develop 120 film, and it would be much more simpler to use 35mm in my 120mm Diana. This is a simple and free method of using 35mm film in a 120 camera.
Step 1: What you need
All you need for this is:
~ One used roll of film.
~ A 120mm film spool
~ Some buttons or something that can be used as a spacer underneath the roll to hold it in place.
~ Obviously a new roll of film, in this Intsructable I am using some Kodak slide film.
~ A 120 camera, I am using the Diana, but I'm pretty sure you can use any 120 camera, but it depends whether the 35mm film will fit
~ Some kind of wire cutters or other cutters that you can cut the plastic.
Step 2: cutting up the 120 spool
I noticed that a 120 spool has 2 perfect columns to fit into a 35mm film windy-hole.
Cut the 120 spool in halve, to make two 35mm holders, In the picture you can see the original spool, and the modified holder made from it. You have to cut it so that there is only two spikes that come up above the rest, like the detailed pictures. You must also make the spikes less wide, so that they fit snuggly into the 35mm windy hole.
Step 3: Fitting the modified holder.
Once cut correctly it should slide quite well into your film, the top photo is the take-up roll, it has already been finished and the new roll will be taped and wound into it as your roll progresses.
The second picture is the other modified holder, used for the original film, it has a rubber band wound in there so that it sits in the right place.
The third picture is both the films with the modified winders, The left will be taped onto the right and pulled into it.
Step 4: Spacers
Spacers are needed so the films don't fall down when you put them in the camera, I am using some buttons but you can pretty much use anything you can find around the place to make it fit.
Step 5: Loading the film
Put your film into the camera with the winders and then put in the spacers, tape the left film onto the right and wind it until you know its in there and secured.
Step 6: Loading film, Extended.
On the back of the camera there is a red frame number box, I made this mistake and forgot to tape over it.
You have to cover this in electrical tape or something light proof to prevent your film being flooded by light leaks.
Step 7: Shoot away!
Now you can go and shoot, remember your framing as it will be different to what you see in the viewfinder. Below is a cross processed picture from a 35mm roll I shot on the Diana.