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> Is anyone using Ilfords new receprocity formula ? |
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#12
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First calculate the metered exposure without the filter - 1/60th in your example Then adjust for the filter to give 15 seconds - this is in effect your metered exposure. The reciprocity factor for the appropriate film needs to be applied to the 15 seconds in your example. Hope this helps |
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There's an Android App that allows for reciprocity failure with filters added.
Ian |
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These are the factors you use for each film. You need a scientific calculator. There is one on an iPhone if you press the calculator button and turn the phone on it’s side. You enter the number of seconds measured exposure, press the Xy (X with a small y top right) button, then key in the number from the chart above, followed by the = sign, and you get the corrected exposure. It’s easier to do this than describe it in writing! Alex Sent from my iPhone using Tapatalk Pro |
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Should have added the App does bellows extension factor, filter density adjustment as well as reciprocity factor in all together. Ian |
#17
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For FP4+ and 15 Secs...
Exposure = X↑Y = 15↑1.26 = 30 Secs
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Cheers, Barry |
#18
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The new formula does give shorter times than the previous one. I use a chart that Les Maclean posted in this forum years ago. I prefer the results it produces. Using the new formula for long exposure work with, for example, a x10 stop filter I had less shadow detail.
I’ve posted Les’s old chart, for box speed FP4, it is more in line with the older Ilford times. Together with a 10-15% reduction in development times it gives me good results. Always best to experiment and arrive at your own exposure times based on your working methods. Metering for long exposure work is subjective anyway and will always be dependant on the lighting conditions. |
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Which film are you using?
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