Reciprocity Failure of Instax ISO800 Film

I have an instax back for my rz67 and wanted to try some night photography. Has anyone experimented with long exposures using this stuff or any exposures at least 1-2s long?

I think I read somewhere to add up to 3 stops for a 60 second exposure.

Which film back did you get?

Based on my own limited experience doing long exposures (past 1s) with Instax, I'd say it has severe reciprocity failure, far worse than any negative film I've ever used. I haven't spent the film needed to quantify that rigorously, but I've seen anecdotal claims ranging as high as ten stops for pinhole exposures of a few seconds.

If you intend to pursue this seriously, plan on spending a few packs of film up front on controlled tests to come up with a guide for the kinds of scenes you typically want to photograph.

"10 stops over" woah!! - good to know I think I'll just get a flash lol. I am using a back built for the RZ67 called "Zinstax" by this guy named haan.chen on instagram. He makes them out of sq6 camera backs and im 10 packs in and it works like a charm.