too large

I was finding the area of 35mm, as I was having to mask into 20mm squares, a little smaller than optimal.

I tried 120 (6x7 back on my 5x4) - but I've gone too big for the circular patterns - the ones I've not managed to project yet!  The negs are about the size of the whole slide area so I'll have to experiment to see how much area I can actually project