Pretending not to know what is on your film can be really thrilling!
There are different film types and Diana F+ usually takes 120 film, but there are 220 films too and that means the film is twice as long. That is only possible because the paper back is missing, so it is as unprotected as any 35mm film and the red window will burn your film to zero if you don’t… well… that is the technique and the trick!
You insert the 220 film, close the Diana and start advancing ’till you see the paper from the beginning gets shiny and becomes plastic. There you got the film. Now be fast and tape the red window as good as possible to avoid EACH and EVERY light leak. Best thing is to do all that in a bit darker place and NOT in bright sunlight!!! As you have taped the back and there are no paperback numbers to guide you, anyways you can advance it just as you normally would. A bit, a bit more, still a bit further – you will not know beforehand what is on the film, how the single shots will overlap or not. It is big fun!
Of course you can do it with 120 films, too. Just tape the red window so you cannot see the numbers and shoot, advance a bit and go on…The good and interesting thing is, that there is no paper on the back- you can easily make a redscale film out of 220 films! Just turn it around and advance till you see the (white) plastic, tape it very well and shoot like you want to.
This tip works for all medium format cameras!