Response to the zone system and the use of filters

We have been talking about sensitivity of film and exposure meters so far, but somehow not about the device that has the largest influence: The filter itself. There is -- as far as I am aware -- no norm of any sort designating B&W filters. You will say that there are Wratten numbers, Schott numbers, Heliopan number, Cokin numbers etc. (and even lists telling you which wratten number ought to be the corresponding Schott number etc. ) designating each filter, but in fact the variations in density (easy to measure with an exposure meter) and colour (easy to see in a direct comparison between two filters supposedly "identical") are huge. Kodak may be able to suggest Wratten filters for a specific film, but this information will not necessarily (or most likely) work with different filters. Again I must say that bracketing is the only workable solution for red filters, since so many different aspects are involved beyond film sensitation, filter density and colour and colour accuracy of the exposure meter -- far to many to keep in mind or even to think about while trying to previsualize.

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