You can also try: Provia 100F, Velvia 100F and Velvia 100, those are also in production. But, no need to test Velvia 100F and Velvia 100, those have even less exposure latitude than Velvia 50. Then again, Provia 100F has more and is a very sharp and fine-grained film. If you can get some Astia 100F, which may or may not be discontinued, it has the widest exposure latitude in Fuji's reversal film range. I would go with Astia 100F if you can get it and if ISO 100 is enough for your purpose. It's definitely the one for the situation you describe.