Reciprocity failure is the films decrease in light sensitivity with increased length of exposure time... when it is pushed beyond the limits of it's exposure range.... Generally one only has to worry about this at night... I can't imagine that you would have a problem with this shooting during daylight hours. Unless you are shooting waterfalls, why would you need 2-4 second exposure times? Shoot at a moderate apertures (as opposed to f/22 or f/32) and you should be able to obtain shutter speeds of reasonable time. Reciprocity failure usually occurs at shutter speeds below 1/10 of a second. The rule of thumb (always best to consult the films data sheets) is a doubling of exposure time. So if you were shooting at 2 seconds you would want to double your exposure time more to say 4 seconds..... 4 seconds to 8 seconds..... of course as I already said this is just a generalization.... consult the film manufacturers website, or do a google search... you may come up with some charts or recommendations.

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