


reciprocity for bergger bpf 200 shot @100
Does anybody have any experience with reciprocity failure with bergger bpf 200 shot at 100asa? If so, do you happen to know the correction times? Or can someone direct me to the times?
Thanks,
Todd

Originally Posted by toddstew
Does anybody have any experience with reciprocity failure with bergger bpf 200 shot at 100asa? If so, do you happen to know the correction times? Or can someone direct me to the times?
Thanks,
Todd
To 1/2 second  no adjustment
1 second  1.5 stops
10 seconds  3 stops
100 seconds  4 stops

thanks jandc. Pardon my dumb question, but how would that transfer to time? 1.5 stops equals how much time increase if I want to keep the same fstop? Would 10 seconds become 30 seconds?

Originally Posted by toddstew
thanks jandc. Pardon my dumb question, but how would that transfer to time? 1.5 stops equals how much time increase if I want to keep the same fstop? Would 10 seconds become 30 seconds?
each additional stop is a doubling of the time  so yes, 10 becomes 30 seconds.

Thank you for the illumination(yuk,yuk)
Todd

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Oops ther is a math error here.
If the exposure is 10 seconds a simple calculation would be 40 seconds (10x2=20;20x2=40)
However, I believe you will find that amount of time insufficient because the reciprocity for 40 seconds now comes into play. 3 stops is 2 raised to the third power, or 8. At the very least then, the time requirted would be 80 seconds.
To find out for sure, make 3 exposure, one at 40 seconds, one at 80 and one at 160 seconds. These are one stop apart and yuo will learn a lot about the reciprocity of the film. In fact, if you have a densitometer you will have enough information to make a graph of the reciprocity curve from which you can calculate the reciprocity for any given amount of time.


Originally Posted by Jim Noel
Oops ther is a math error here.
If the exposure is 10 seconds a simple calculation would be 40 seconds (10x2=20;20x2=40)
However, I believe you will find that amount of time insufficient because the reciprocity for 40 seconds now comes into play. 3 stops is 2 raised to the third power, or 8. At the very least then, the time requirted would be 80 seconds.
To find out for sure, make 3 exposure, one at 40 seconds, one at 80 and one at 160 seconds. These are one stop apart and yuo will learn a lot about the reciprocity of the film. In fact, if you have a densitometer you will have enough information to make a graph of the reciprocity curve from which you can calculate the reciprocity for any given amount of time.
Opps one more math error. A ten second second exposre increased by three stops results in an 80 second exposure. Metered timeX2^number of stops=correct exposure. 10x2^3=80. This formula almost never fails.
Christopher Breitenstein
Last edited by chrisofwlp; 03012007 at 12:05 PM. Click to view previous post history.

Am I crazy? Look at ilford's hp4 reciprocity specs here>http://www.ilfordphoto.com/Webfiles/...6115141521.pdf. A metered 10 secs is recommended to be adjusted to about 30 seconds. According to their chart this mean "times 3" ... not a quantum ride of additional 3 "stops", or 10>20>40>80 sec.
Haven't done dark light above 8 seconds metered, but about x3, or 24 sec of exposure works fine at that level of the curve. Sure would like to know how far out in left field and/or lucky I am!! ;•]
Bruce

