In GUP#31 its all about experimental photography. Experimental photography includes alternative process techniques, and broadly refers to any photographic process or product falling outside the realm of straight film or digital photography. However, that comes close to a definition. It may be more appropriate not to define what 'experimental photography' is (or isn't).
From Man Ray to Stephen Gill, and from Picasso to Kenji Hirasawa, they are all represented in this issue to some extent. Although they vary greatly in goal and scale, experiments always rely on repeatable procedure. At least, that's what becomes apparent when delving into the history of photographic experiments.
While they are truly original in their own right, the works of Harold Strak, Sebastiaan Bremer and Taisuke Koyama, among many others in this edition of GUP, also fit within a long tradition of photographic experimentation.