Dear friends, Can I find that Ilford reciprocity failure table on the web? On which sites ? Is there a similar table for T-max 100 ? Reciprocity failure is really a problem. What if I'm working with lith film for half tone development later on ? Thank you for any help.
Ricardo. ----- Original Message ----- From: Guillermo <pen...@home.com> To: <pinhole-discussion@p at ???????> Sent: Monday, September 17, 2001 2:34 PM Subject: Re: [pinhole-discussion] Determining exposure beyond..................... > > ----- Original Message ----- > From: "Rune Tallaksen" <tall...@alfanett.no> > > > Can anybody help me with how to determine exposure when correcting for > > resiprosity failure when the measured esposuretime exceeds that of the > table > > from the filmvendor? > > > > For instance when using Ilford HP5 Plus, the film data sheet gives the > added > > time for resiprosity failure until initial measured 35 secs(corrected for > > pinhole f stop). How can I calculate the "correct" exposure time beyond > this > > point? Tiral and error until now has not been satisfactory for me. > > One way to do it is by extrapolating the curve Ilford is giving you. You > can do that mathematically or graphically. I usually do it graphically. > Take the Ilford curve and reproduce it on a piece of paper, extend the "X" > or horizontal axis to read the maximum "uncorrected" time you want and then > extend the curve with pencil trying to follow the same tendency, then is > just a matter of extending the "Y" axis and graduating both axis. I just > did that very quickly and the resulting extended curve gives me the > following values, for 60, 90 and 120 secs of uncorrected exposure: > > 60 secs uncorrected = 475 secs corrected > 90 secs = 925 secs > 120 secs = 1900 secs > > Once you have the extrapolated curve, use it and if you get consistently > somewhat overexposed film, that means the curve was done a bit to steep. If > film is underexposed consistently then the curve needs to be re-done a > little more steeper. > > One thing for sure, extrapolating the curve would give you better > reciprocity corrections than "trial and error". > > Hope it helps. > > Guillermo > > > _______________________________________________ > Pinhole-Discussion mailing list > Pinhole-Discussion@p at ??????? > unsubscribe or change your account at > http://www.???????/discussion/ >
