Provia 100F - along with its faster brother Provia 400X - has rapidly become one of my favourite films for colour photography, and providing I'm expecting decent light, it's rare that I'm not carrying at least one roll of it in my bag.
Firstly, let’s talk about how most people on here would probably use it – cross processing. The colour shift of Provia 100F is towards cyan, but any bold reds, yellows or blues will really stand out, given the right conditions. It could also, like a lot of films when cross-processed, benefit from a slight bit of underexposure to prevent blown-out highlights. It’s a fairly similar slide film to Sensia 400 in this respect. I’d like to point out, though, that don’t think Provia 400X reacts the same – it’s a totally different emulsion which barely colour shifts at all.
However, while this is a nice effect, it’d be a shame to never explore the way it was intended to be used. Provia 100F, when E6-processed, gives you amazing, rich, vibrant colours, but without the over-saturation of Velvia 50. It reproduces skin tones far more accurately than Velvia, too. The one problem with it is that it has been known, on occasion, to take on a strange bluish cast; it’s very rare, and providing you’re not intending to project the slides it should be easy enough to remove in post-processing, but it’s one thing to consider.
And, of course, if your only experience of colour photography is colour negative film, you’ll be amazed by how much more vivid and clear everything looks. Just be prepared – slide film is a more tricky material to work with. While it can be used in a Holga in the right conditions (decent sunlight at f/11 or slightly cloudy at f/8), be aware that even a single stop of underexposure can make slide film pretty much unusable. You’re much better off using it in an automatic camera like an XA2, LC-A or Olympus Trip, or in a fully manual camera with a light meter (like any decent TLR, SLR or rangefinder).