Hi everyone. After I worked out the reciprocity characteristics for efke 25 I thought I'd check out its response to filters. All filters were Kodak Wratten gels that I use most often in the field. As I suspected the manufacturer's factors cannot be trusted AND development compensation is necessary (at least with the filters that I commonly use). The filter number is listed followed by exposure compensation and then development effect (expressed in zone system parlance). Here are my results:
#47: 6x (+2 2/3 stops) N-2/3
#58: 4x (+2 stops) N+1/3
# 8: 1.2x (+1/3 stop) N-1/3
#12: 1.5x (+2/3 stops) N-1/3
#15: 1.5x (+2/3 stops) N-1/2
#21: 3x (+1 2/3 stops) N-1/2
#25: 4x (+2 stops) N-2/3
I hope you understand what I meant by development effect. All development times for my testing were N times. So with the #47 filter, N development gave me a negative as if I had actually given N-2/3. So if I were out in the field using say, the # 25 and N development were indicated, then I would have to give N+2/3 to get contrast back to N. If N-1 were indicated, then I would have to actually give N-1/3. If I actually gave the indicated N-1 then I would end up with N-1 2/3. Hope this makes sense! I'm beat....I need a cup of tea!
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